Design of components for casting


Why should we use casting?



Complex parts which are difficult to machine, are made by the casting process.
Almost any metal can be melted and cast. Most of the sand cast parts are made of cast iron, aluminum alloys and brass.
The size of the sand casting can be as small as 10g and as large as 200x103kg.
Sand castings have irregular and grainy surfaces and machining is required if the part is moving with respect to some other part or structure.
Cast components are stable, rigid and strong compared with machined or forged parts.
Typical examples of cast components are machine tool beds and structures, cylinder blocks of internal combustion engines, pumps and gear box housings.


Basic considerations of casting:
  • Always keep the stressed areas of the parts in compression 
  • Round all externalcorners
  • Wherever possible, the section thickness throughout should be held as uniform as compatible with overall design considerations
  • Avoid concentration of metal at the junctions 
  • Avoid very thin sections
  • The wall adjacent to the drilled hole should have a thickness equivalent to the 
thickness of the main body
  • Oval-shaped holes are preferred with larger dimensions along the direction of 
forces
  • To facilitate easy removal, the pattern must have some draft
  • Outside bosses should be omitted to facilitate a straight pattern draft

 Always keep the stressed areas of the parts in compression
· Cast iron has more compressive strength than its tensile strength.
· The castings should be placed in such a way that they are subjected to
compressive rather than tensile stresses.
                        ·  When tensile stresses are unavoidable, a clamping device such as a tie rod or a bearing cap should be considered.
                        ·  The clamping device relieves the cast iron components from tensile stresses.
 Round all external corners
   It increases the endurance limit of the component and reduces the formation of 
brittle chilled edges. 
                        ·  When the metal in the corner cools faster than the metal adjacent to the corner, brittle chilled edges are formed.
                        ·  Appropriate fillet radius reduces the stress concentration.
Wherever possible, the section thickness throughout should be held as uniform as compatible with overall design considerations
Abrupt changes in the cross-section result in high stress concentration.
 If the thickness is to be varied at all, the change should be gradual
           Avoid concentration of metal at the junctions
     At the junction, there is a concentration of metal.Even after the metal on the surface solidifies, the central portion still remains in the molten stage, with the result that a shrinkage cavity or blowhole may appear at the centre.
            There are two ways to avoid the concentration of metal.
            One is to provide a cored opening in webs and ribs. Alternatively, one can stagger the ribs and webs.
            Avoid very thin sections
   It depends upon the process of casting such as sand casting , permanent mold
            castingor die casting
         The wall adjacent to the drilled hole should have a thickness equivalent to the  thickness of the main body
    The inserted stud will not restore the strength of the original thickness.
     Oval-shaped holes are preferred with larger dimensions along the direction of forces
      To facilitate easy removal, the pattern must have some draft
· A minimum draft of 3° should be provided.
          Outside bosses should be omitted to facilitate a straight pattern draft

Material Selection in Machine and Product Design



Selection of a proper material for the parts/components is one of the most important steps in the process of machine and product design.
The best material is one which will serve the desired purpose at minimum cost.
It is not always easy to select such a material and the process may involve the trial and error method. 



The factors which should be considered while selecting the material for a machine component are as follows:
  • Availability 
  • Cost 
  • Mechanical Properties 
  • Manufacturing Considerations 
  • Design / Product finishing


1. Availability:

The material should be readily available in the market, in large enough
quantities to meet the requirement.
Cast iron and aluminium alloys are always available in abundance while
shortage of lead and copper alloys is a common experience.


2. Cost:

Cost For every application, there is a limiting cost beyond which the designer cannot go. When the limit is exceeded, the designer has to consider other alternative materials. In cost analysis, there are two factors, namely cost of material and cost of processing the material into finished goods.
It is likely that the cost of material might be low, but the processing may involve costly manufacturing operations.


3. Mechanical Properties:

Mechanical properties are the most important technical factor governing the selection of material. They include strength under static and fluctuating loads, elasticity, plasticity, stiffness, resilience, toughness, ductility, malleability and hardness. Depending upon the conditions and the functional requirement, different mechanical properties are considered and a suitable material is selected.
The piston rings should have a hard surface to resist wear due to rubbing action with the cylinder surface, and surface hardness is the selection criterion.
In case of bearing materials, a low coefficient of friction is desirable while
clutch or brake requires a high coefficient of friction.


4. Manufacturing Considerations:

In some applications, machinability of material is an important consideration in selection. Sometimes, an expensive material is more economical than a low priced one, which is difficult to machine.
Free cutting steels have excellent machinability, which is an important factor in their selection for high strength bolts, axles and shafts.
Where the product is of complex shape, castability or ability of the molten metal to flow into intricate passages is the criterion of material selection.
In fabricated assemblies of plates and rods, weldability becomes the governing factor.
The manufacturing processes, such as casting, forging, extrusion, welding and machining govern the selection of material.


5. Design / Product Finishing: 

In some cases the final Product demands a finishing surface, or in some cases, a functional feature that could only be obtained using materials that are very expensive because they difficult to produce or extremely rare to find. That will be, of course, noticeable on the final product price. 









Mechanical Properties of Metals


The mechanical properties of the metals are those which are associated with the ability of the material to resist mechanical forces and load.
Often materials are subject to forces (loads) when they are used. Mechanical engineers calculate those forces and material scientists how materials deform (elongate, compress, twist) or break as a function of applied load, time, temperature, and other conditions.



Materials scientists learn about these mechanical properties by testing materials. Results from the tests depend on the size and shape of material to be tested (specimen), how it is held, and the way of performing the test. That is why we use common procedures, or standards.


1. Strength: 

It is the ability of a material to resist the externally applied forces
without breaking or yielding.
The internal resistance offered by a part to an externally applied force is
called stress.

2. Stiffness:

It is the ability of a material to resist deformation under stress.
The modulus of elasticity is the measure of stiffness.

3. Elasticity:

It is the property of a material to regain its original shape after
deformation when the external forces are removed.
This property is desirable for materials used in tools and machines.
It may be noted that steel is more elastic than rubber.


4. Plasticity:

It is property of a material which retains the deformation produced under load permanently.
This property of the material is necessary for forgings, in stamping images on
coins and in ornamental work.


5. Ductility:

It is the property of a material enabling it to be drawn into wire with
the application of a tensile force.
The ductility is usually measured by the terms, percentage elongation and
percentage reduction in area.
The ductile material commonly used in engineering practice (in order of
diminishing ductility) are mild steel, copper, aluminium, nickel, zinc, tin and
lead.

6. Malleability: 

It is a special case of ductility which permits materials to be rolled or
hammered into thin sheets.
The malleable materials commonly used in engineering practice (in order of
diminishing malleability) are lead, soft steel, wrought iron, copper and
aluminium.


7. Brittleness:

 It is the property of a material opposite to ductility. It is the property
of breaking of a material with little permanent distortion.
Brittle materials when subjected to tensile loads, it snaps off without giving
any sensible elongation.
For example, cast iron is a brittle material.


8. Toughness: 

It is the property of a material to resist fracture due to high impact loads like hammer blows.
The toughness of the material decreases when it is heated.
It is measured by the amount of energy that a unit volume of the material has
absorbed after being stressed upto the point of fracture.
This property is desirable in parts subjected to shock and impact loads.


9. Machinability:

It is the property of a material which refers to a relative case with which a material can be cut.


10. Resilience:

 It is the property of a material to absorb energy and to resist shock and impact loads.
It is measured by the amount of energy absorbed per unit volume within elastic limit.
This property is essential for spring materials.


11. Creep: 

When a part is subjected to a constant stress at high temperature for a long period of time, it will undergo a slow and permanent deformation called creep.
This property is considered in designing internal combustion engines, boilers
and turbines.


12. Fatigue: 

When a material is subjected to repeated stresses, it fails at stresses below the yield point stresses. Such type of failure of a material is known as fatigue.
The failure is caused by means of a progressive crack formation which are usually fine and of microscopic size.
This property is considered in designing shafts, connecting rods, springs, gears, etc.


13. Hardness:

 It is a very important property of the metals and has a wide variety of meanings.
It embraces many different properties such as resistance to wear, scratching,
deformation and machinability etc.
It also means the ability of a metal to cut another metal.
The hardness is usually expressed in numbers which are dependent on the
method of making the test.
The hardness of a metal may be determined by the following tests:

(a) Brinell hardness test, (b) Rockwell hardness test,

(c) Vickers hardness test and (d) Shore scleroscope.





References : Introduction to machine design, SUNIL G. JANIYANI, Darshan Institute of Engineering & Technology, Rajkot
   

Some Interesting Upcoming Conferences

Hi Everyone! 

Today I´ll do a list with some upcoming conferences with various interesting themes. They are mainly within Mechanical Engineering but in future posts I´ll try to keep up and give you dates from other areas of interest! 
So, here we go : 


3D Printing Europe 2018
11 Apr 2018 - 12 Apr 2018 • Berlin, Germany
Event website:
http://www.idtechex.com/3d-printing-europe/show/en/

Functional Powder Metallurgical Components in Next Generation Electric Cars
16 Apr 2018 - 17 Apr 2018 • Jülich, Germany
Event website:
http://www.epma.com/seminars

Hybrid Materials and Structures 2018 — 3. Internationale Konferenz: „Hybrid Materials and Structures 2018“
18 Apr 2018 - 19 Apr 2018 • Bremen, Germany
Event website:
https://hybrid2018.dgm.de

High Performance Machining Technology Conference 2018
24 Apr 2018 - 25 Apr 2018 • Chongqing, China
Event website:
http://www.ringierevents.com/conference/17344

RAS — Robotics and Autonomous Systems 2018
25 Apr 2018 - 26 Apr 2018 • London, United Kingdom
Event website:
http://www.robotics-autonomous.com/coms

3rd International Conference on 3D Printing in Medicine
04 May 2018 - 05 May 2018 • Halle, Germany
Event website:
http://3dprint-congress.com/

HTSMAs — 2nd International Conference on High Temperature Shape Memory Alloys
15 May 2018 - 18 May 2018 • Irsee, Germany
Event website:
https://htsmas2018.dgm.de/

Unmanned Systems Technology
16 May 2018 - 17 May 2018 • London, United Kingdom
Event website:
http://www.umsconference.com/coms

Technology Hub — The professional event of innovative technologies
17 May 2018 - 19 May 2018 • Milan, Italy
Event website:
http://www.technologyhub.it/en


ICRA — IEEE International Conference on Robotics and Automation
21 May 2018 • Brisbane, Australia
Event website:
http://www.icra2018.org/

AQTR — 2018 IEEE International Conference on Automation, Quality and Testing, Robotics
24 May 2018 - 26 May 2018 • Cluj-Napoca, Romania
Event website:
http://www.aqtr.ro/

REMOO 2018 — The 8th International ENERGY Conference & Workshop
29 May 2018 - 31 May 2018 • Venice, Italy
Event website:
http://remoo.eu/

EMI 2018 — Engineering Mechanics Institute Conference
29 May 2018 - 01 Jun 2018 • Cambridge, Massachusetts, United States
Event website:
https://umi.mit.edu/EMI2018

Rotordynamik - Schwingungen in rotierenden Maschinenteilen
07 Jun 2018 - 08 Jun 2018 • Berlin, Germany
Event website:
https://www.hdt.de/W-H110-06-145-8

SME — 2018 International Symposium on Electrical Machines
10 Jun 2018 - 13 Jun 2018 • Andrychów, Poland
Event website:
http://www.sme2018.agh.edu.pl

AIVELA 2018 — 13th Intl Conference on Vibration Measurements by Laser and Noncontact Techniques
20 Jun 2018 - 22 Jun 2018 • Ancona, Italy
Event website:
http://www.aivela.org/13th_Conference/index.html

AI4I — 2018 First International Conference on Artificial Intelligence for Industries
18 Jul 2018 - 20 Jul 2018 • Laguna Hills, CA, United States
Event website:
http://www.ai4i.org

Biorob — 2018 7th IEEE International Conference on Biomedical Robotics and Biomechatronics
26 Aug 2018 - 29 Aug 2018 • Enschede, Netherlands
Event website:
http://www.ieeebiorob2018.org

IROS — IEEE/RSJ International Conference on Intelligent Robots and Systems
01 Oct 2018 - 05 Oct 2018 • Madrid, Spain
Event website:
https://www.iros2018.org/calls

IC-RIDME 2018 — International Conference on Recent Innovations and Developments in Mechanical Engineering
08 Nov 2018 - 10 Nov 2018 • Shillong, India
Event website:
https://icridme.wixsite.com/nitm-icridme2018


GrabCAD - Alstom Challenge Submission

Hi everyone!

As promised I will make a post regarding Creating Machines submission on Alstom Engineering challenge promoted by GrabCAD !
This is the last day for ideas submission and a lot of cool stuff is already submitted!
So, lets start explaining the main objective of the contest. The objective is to reduce the weight and the manufacturing cost of the CVS and battery box support that already exists on Metropolis City Train. You need to accomplish the Norms given (challenge´s attached documentation) and use only the available volume (restricted volume also in the attached documentation).

Now lets go to my idea. 

This structural support is a welding construction based on the design of some building and bridge structures and on some aircraft structures as well.
Every component is made of laser cutting sheet metal parts. 
The material can be normal S235JR Steel but for more resistance other materials can be used, for example S275J2G3 or S355J2G3 (1.0570). 











The thickness of the main body is 6mm. Lower the thickness of the main body can surely be possible and lower the total weight can be achieved, but I really think that a total weight of 28,8kg is way better when compared to the actual support weight (56,5kg). 

A complete set has a total of 144 kg (Alstom´s actual set has 282,5kg), there is no need to change the bolt joint support on the train solebar and it fits perfectly on the available volume. 





The welded construction can take more time but on the other hand, combined with folded sheet metal steel makes it more stable and reliable. With some changes on the design it can also be used riveted connections like it is used on bridges and skyscraper construction or even on aircraft Industry.

The design accomplishes the standard Norms (EN12663; EN61373; Alstom Standard ENG-STD-003; EN 45545-2).



Unfortunately, due to lack of time is impossible to present more variations to this design, but I’m extremely happy with this design in particular and with the overall result and I really believe that this structure is something that can be putted on practice and has a realistic vision on which design, safety and overall feasibility is concerned.

For more detailed information about the contest and to see other submissions go to: https://grabcad.com/challenges/redesign-the-structural-support-of-the-metropolis-metro-underframe


All 3D files are available for download here on Creating Machines, just go to the Downloads field on the very top of the Blog. 










Alstom launches an engineering challenge on GrabCAD

GrabCAD Community Website has launched together with Alstom partnership, a contest to develop a new structural battery support for a city train ( Metropolis Metro ). 
Anyone that is registered on GradCAD can participate. 
Just need to follow all the rules, come up with a new solution and present it along with 3D files, some fotos and a text explaining what advantages does the solution bring. 


Note : You can submit more than one solution  during the contest. 

The deadline is March 26th, 2018. 
The prizes are :

1st place -    6.000$ 
2nd place -   4000$
3rd place -   2000$

For more informations and 3D files visit : 

Creating Machines is going to submit a solution as well and I will share it with you on my next post. 

Submit yours too!! What are you waiting for?? 
" Think Mcfly!! Think!! "

Design for Manufacturing and Assembly (DFMA)- Part two

Design for Manufacturing and Assembly ( DFMA ) -  Guidelines






1. Reduce the Part Counts:



· Design engineers should try for product design that uses the minimum number 
of parts. 


· Fewer parts result in lower costs. 


· It also makes assembly simpler and fewer chances of defects. 


· Minimize part count by incorporating multiple functions into single parts.







One method for determining minimum part quantities is to first list out all the components in your assembly, including hardware. Then ask the following questions:



Can the part be manufactured using the same material as other parts?

How does the part in question move in relation to other moving parts?

Can the parts be combined without need for any special process or tooling?

If combined with another part how does that impact ease of possible disassembly?

If combined with other parts how would it impact ease of manufacture?



Through reduction of component part quantities, you also reduce the amount of hardware and the number of assembly steps required. The likelihood of assembly errors are subsequently reduced in relation to the reduction in assembly steps.



2. Use modular designs:



Modular design is becoming more prevalent in many industries. It has various advantages for the manufacturer, the dealer and the customers. Some of the advantages to modular design are listed below:



· Modularize multiple parts into single sub-assemblies. 


· Modular design reduces the number of parts being assembled at any one time 
and also simplifies final assembly. 


· Field service becomes simple, fast and cheap because dismantling is faster and 
requires fewer tools. 




· Modules help minimize cost by reducing the number of different parts within a family of products

· Modules may result in shorter learning curves when new employees require training on the assembly of the products

· In some cases, it allows the manufacturer to balance production throughout the year based on projected seasonal sales

· In addition, the dealer can stock most sold items for fast delivery to customer. Customized combinations of the modules can be delivered to the site and installed quickly.

· Modules allow for greater outsourcing of parts and assembly modules, freeing-up manufacturing capacity and increasing the number of products delivered on time

· Modules provide for easy and quick installation of products at the site saving labor and time

· Modular assemblies can also be improved with minimal effect on the rest of the product





3. Assemble in the open:



· Design to allow assembly in open spaces, not confined spaces. 


· Assembly operation should be carried out in clear view. This is important in 
manual assembly. 


· Always allow for adequate tool clearance and assure the operator can see what they are assembling, with no hidden interfaces or attachment points.



4.Optimize part handling:



· Design parts so they do not tangle or stick to each other or require special

handling prior to assembly.



5. Do not fight gravity:



· Design products so that they can be assembled from the bottom to top along 
vertical axis. 


· Design the first part large and wide to be stable and then assemble the smaller 
parts on top of it sequentially. 






6. Design for part identity (symmetry):



· Symmetric parts are easy to assemble. 


· Maximizing part symmetry will make orientation unnecessary. 


· Features should be added to enhance symmetry wherever required. 




7. Eliminate Fasteners:



Threaded bolts, washers and nuts are time consuming to assemble. If they are required, consider weld nuts or nuts that are captured in the part. The designer must look at alternative methods of attachment.

Minimize the variety of hardware required for assembly



· Fasteners are a major obstacle to efficient assembly and should be avoided 
wherever possible. 


· They are difficult to handle and can cause jamming, if defective. 


· If the use of fasteners cannot be avoided, limit the number of different types of 
fasteners used. 


· Consider the use of connections integrated into the parts such as snap fit or tab and slot

· Evaluate other bonding techniques with adhesives

· Match fastening techniques to materials and product functional requirements

· Consider ease of disassembly for service and repairs



8. Design parts for simple assembly:




There are many methods to design for ease of assembly. When designing for assembly, remember the simpler the design the easier it is to assemble. The designer should consider where the assembly is going to be performed and the tools or equipment that will be available. For example, if the product is sold as a kit and assembled in the field by the customer, it is different than if it will be assembled on an assembly line or in a work cell. There are many guidelines for ease of assembly. The following list contains some examples:

· Incorporate simple patterns of movement in your assembly process and minimize steps. If that is not possible, consider breaking it down into logical sub-assemblies.

· Avoid multiple set-ups or re-orientation during the assembly process. This creates wasted movement and time.

· Parts should incorporate lead-in features and chamfers. This allows for easier insertion of pins or bolts.





9. Parts should easily indicate orientation for insertion:




· Parts should have self-locking features so that the precise alignment during assembly is not required or provide marks (color) to make orientation easier.



The design engineer should consider how the parts are going to be handled and oriented during the manufacturing and assembly processes. If this is not done, the impact could range from non-value-added motion and part movement to possible operator safety issues or requirements for special fixtures or lifting devices. There are several basic principles that can be applied to improve parts handling and orientation. A few examples can be found below:

· Drawings should consistently indicate the proper origination when fed into a process. An example would be how parts are oriented into a brake press for either bend up or bend down operations.

· The designer should avoid use of parts that can easily become tangled in the container or that are difficult to pick up and handle. This slows production and can increase waste due to damaged, dropped or lost parts.

· When possible, design parts that are symmetrical along both axis. This allows for ease of fabrication and correct assembly.

· Parts should be designed so that they may be easily grasped, oriented and placed in an assembly or weld fixture. Examples would be parts with flat, parallel surfaces that are easily picked-up and assembled by the operator. Another instance to think about could be if the part is picked up by a suction or magnetic gripping device when used in a “pick and place robot” application.

· Always avoid parts with sharp edges, burrs or points. Use radii and chamfers when possible to reduce chance of operator injury.

· Avoid heavy or oversized parts that will require lifting devices or may increase worker fatigue and risk of injury. Always consider assembler and operator safety in all designs.

· When designing a workstation, it is good practice to plan for minimum worker travel time. Minimize the distance to access and move a part or assembly. A good rule of thumb is that most components should be within two steps from the point of assembly and common hardware and tools within easy reach.





10. Standardize parts to reduce variety:



· Using the same commodity items such as fasteners can avoid errors. 


· It also reduces the cost. 




11. Color code parts that are different but shaped similarly:




· Distinguish different parts that are shaped similarly by non-geometric means, such as color coding.




12. Design the mating features for easy insertion:



· Add chamfers or other features to make parts easier to insert.



13. Provide alignment features:



· Design parts with orienting features to make alignment easier.





14. Place fasteners away from obstructions:



· It is better to locate fasteners in place where one has access to the fastener.



15. Deep channels should be sufficiently wide to provide access to fastening tools:







16. Provide flats for uniform fastening and fastening ease:



· Do not fasten against angled surfaces.



17. Design Parts for Ease of Fabrication



The designer should consider the method of fabrication that may be used for producing the parts, the required material specifications and required production volumes. Some particular guidelines to review are as follows:

· Specify materials that are commonly used and compatible with existing production processes that will minimize processing time and will meet all functional requirements

· Review the part and eliminate unnecessary features that could result in additional process steps, extra effort and complex or expensive tooling

· Design reviews with members of process engineering, quality control and the fabrication team are beneficial when possible. In most cases the meetings result in a few changes to the design that increase utilization of existing tools or improve machine utilization, preventing the need for capital expenses for special tools. In addition, the meetings improve knowledge transfer of design intent to all levels of the organization.





18. Design for Automated Production



There are many obvious advantages to designing products or parts for automation. A few of them are listed below:

· Increased process throughput or efficiency.

· Improved quality or more predictable process results.

· Consistency in the process output.

· Reduced operator labor costs and indirect labor costs



Something else to consider is the fact that automated production can require less flexibility in design than manual production. The product must be designed so that it can be handled with automated equipment like gripping or magnetic lifting and placement equipment. Avoid any requirements for gripper / tool change. You must also use self-locating parts, simple parts-presentation devices and avoid the need for clamping or securing parts during assembly or processing.



Design for Manufacturing and Design for Assembly are both important and often interwoven and referred to simply as DFMA. The primary goal is to design a product and process to be as efficient as possible. Whether a product is assembled by machines or by operators, the designer and the mechanical engineer should work together to ensure that labor cost, overhead and materials are reduced as much as possible. We should always strive to produce a quality product the first time and every time and Design for Manufacturing and Assembly can help! When DFMA is applied, your company can run at higher profit margins, with higher quality and at a greater level of efficiency.