11:
Manufacturability
Objective Lecture Understand how to Select materials to reduce cost Understand how to Design geometries to reduce costs Understand how tolerances influence cost Understand how to Increase quality and reduce time for project work Methods Class discussion on material selection Class discussion on geometries processes and costs Class discussion on tolerances and manufacturing cost Present tips on how to increase quality and reduce time for project work Reference Material Machinery's Handbook (26th Edition) Allowances and Tolerances for Fits Oberg, E.; Jones, F.D.; Horton, H.L.; Ryffell, H.H. (2000). Machinery's Handbook (26th Edition). (pp. 621-668). Industrial Press. Online version available at: http://www.knovel.com/knovel2/Toc.jsp?BookID=309&VerticalID=0
Assembly (mass production)
http://deed.ryerson.ca/~fil/t/dfmdfa.html http://www.dfma.com/ http://www.efunda.com/processes/machining/drill_design.cfm
Boothroyd and Dewhurst Drilling
Lecture Notes
Manufacturability
Objectives
Understand how to select materials to reduce cost Understand how to design geometries to reduce costs Understand how tolerances influence cost Understand how to increase quality and reduce time for project work
Methods
Class discussion on material selection Class discussion on geometries processes and costs Class discussion on tolerances and manufacturing cost Present tips on how to increase quality and reduce time for project work
Standard parts and Materials
Minimize the number of different kinds of materials and parts
Lecture Notes
Just because it is easy to draw doesn't mean it will be easy to make
Allowances and Tolerances for Fits
http://www.knovel.com/knovel2/Toc.jsp?BookID=309
Ease of fixturing
Reference surface where possible Add features to clamp then machine off
Lecture Notes
Standard tools and fixtures
Design the part to be machined with standard tools and fixtures
Concurrent or simultaneous engineering design
Design the part and the process to make it at the same time 80% of manufacturing costs can be designed into the product before manufacturing sees it Key: Know what the customer wants and what the supplier can manufacture
Assembly (mass production)
http://deed.ryerson.ca/~fil/t/dfmdfa.html
DFA (design for assembly) Self aligning Fool proof Assemble one component at a time Use sub assemblies Integrate features onto part one where possible Use snap fits rather than screws, glues... Boothroyd and Dewhurst http://www.dfma.com/
Lecture Notes
Geometry for machining
avoid Undercuts Sharp inside corners Deep holes
http://www.efunda.com/processes/machining/mill_design.cfm
Drilling
http://www.efunda.com/processes/machining/drill_design.cfm
Specify standard drill bit sizes.
Through holes are preferred over blind holes.
Unusual hole sizes add cost of manufacturing - purchasing and inventory . A blind hole does not provide as much leeway for chip exit and cooling. Operations such as reaming and threading after drilling are more easily conducted on a through hole. Twist drills create cone-bottomed holes and flat-bottom holes cause problems with reaming, etc. Drills for smaller holes tend to break and for convenient mass production, are not recommended.
Avoid flat-bottomed holes.
If possible, do not specify holes that are smaller than oneeighth inches in diameter. Minimize the number of directions on the part that holes must be drilled from.
Drilling cont.
The entrance and exit surfaces of a drilled hole should be perpendicular to the hole axis.
Upon entrance of the drill, the drill tip will wander if the surface that the tip contacts is not perpendicular to the drill axis. Exit burrs will be uneven around the circumference of the exit hole. This can make burr removal difficult.
Drilled Hole Depth:
avoid length to diameter ratios of larger than three . Deeper holes are possible but the drill will tend to wander and possibly break. One way to avoid a deep, narrow hole is to use a stepped entrance. Blind holes should be drilled to a depth 25% deeper than the actual hole in order to provide space for chips.
Lecture Notes
Mike O'Donnell
Machining pockets Avoid cutters less than diameters of ~0.125" Avoid depth 5-8X the cutter diameter Overhang leads to deflection, chatter and breakage
Toby Bergstrom
Work envelope Fixturing Beef
Can the part fit in the machine Can you hold the part in the orientation needed to make the feature needed with enough stiffness to make the cuts
Neil Whitehouse
No square inside corners for milling, Realistic tolerances, know the limits of your machinery (size of parts, speed, tolerances), Know what parts are available off the shelf (no reason to design and manufacture what you can buy and save time and effort)