2015 paper (Manufacturing) Flashcards
With the use of sketches explain steps in a photo chemical machining process as it is applied to the chemical blanking of a flat part? (8)
- Clean raw blank part
- Apply resist by dipping, spraying or painting
- Place negative film on resist
- Expose to UV light
- Develop to remove resist from areas to be etched
- Etching in progress
- Etching process complete
- remove resist and clean part
How does the screen resist method differ from the photographic resist method in chemical machining? (3)
Screen resist
- maskant applied by silk screening method
- maskant is painted onto the work piece surface through a silk or stainless steel mesh
- Embedded in the mesh is a stencil that protects the areas to be meshed from being painted
Photographic resist
- Uses photographic techniques to perform the masking using photosensitive chemicals
- applied to surface and exposed to light through a negative image of the desired areas to be etched
- Areas of the maskant are then removed using a photographic developer.
Discuss how the etch factor is related to the depth of cut in a chemical machining operation (2)
Fe = d/u where Fe = etch factor d = depth of cut u = undercut
- Etching is primarily the penetration into the work but also occurs sideways under the maskant. The effect is called undercut. This must be accounted for in the design of the maskant
- Different work materials have different etch factors in CM
Electro-chemical machining is, similarly to chemical machining, classes as a non-traditional machining technology. explain its principle method of material removal. (3)
-Electrolysis, the reverse of electroplating
-ECM removes metal from a conductive workpiece by anodic dissolution
-Material is depleted from
the workpiece (anode) with the tool (mirror image of desired component shape) being the cathode
-plating of cathode is prevented by depleted material being washed away by fast flowing electrolyte solution in a water solution
2 Reasons why chemical milling is not the preferred choice to generate deep cavities (4)
- Very slow process with small MRR. In order to improve production rates the bulk of the work should be shaped by other processes prior to CM
- Surface finish depends on the depth of penetration and with increasing depth the surface finish becomes worse
- Dimensional inaccuracy increases with deeper cavities due to undercut
Fundamental technologies which were necessary to successfully establish Stereolithography (3)
- high-speed computers
- computer aided design (cad)
- precise motion control
- UV lasers
- photo-curable polymers
Referee’s whistle containing a “pea” and a lanyard hole, similar to Figure Q2(b), is fabricated using the Fused Deposition Modelling technology. Describe how you would build this part (sequence,orientation)
(6)
-As FDM requires a support structure one main consideration apart from achieving dimensional accuracy is to minimise the amount of
=layers (manufacturing time)
=support structure (material cost, time, removal time)
-building the pea requires a thin support structure to the main body of the whistle that can be broken off
-build sequence and support structure which depends on orientation will be different and following needs to be considered to produce part
=open entry for air
=open exit for air outlet
=outer round shaped body
=attachment to build internal ball
=lanyard hole
How does the casting industry make use of Rapid Prototyping (AM) technologies explain two applications using different RP technology (6)
=Pattern making
- “quickcast” pattern making using stereolithography for investment casting
- pattern making for sand casting
=Tool making
- AM technologies use silicone rubbers for mould making used in vacuum casting
- AM technologies use their basic starting material and the mould halves plated with metal coating
- LOM uses sheets of steel or other metal instead of paper
- DMLS to produce metal mould tooling
Discuss the principle difference between the support structures in Fused Deposition Modelling and Stereolithography (3)
Stereolithography
-Support structure uses the same material as the one used to make the
component
-One laser to polymerise component structure and support structure
Fused Deposition Modelling
-Support structure can be generated from a different material than the one used
to make the component
-Support structure can be made of material which is soluble in a solution of
water/detergent
-Multiple print heads allow different materials to be used
Explain how the build packet (build setup) differs between
Selective Laser Sintering and Stereolithography (2)
Selective Laser Sintering
-Build packet for Selective Laser Sintering can be stacked and the entire build
chamber can be used as the uncured powder supports the components
Stereolithography
-Parts made by Stereolithography must originate on the base plate of the build
chamber
-Parts cannot be stacked due to the liquid resin which in its uncured state cannot
be used as support structure
Discuss whether setting up an internal kanban for the delivery of the sheet metal to the aluminium casing manufacturer is a sensible alternative to the current weekly delivery (3)
Benefits
- Production control can order aluminium sheets based on actual usage; prevents guessing using MRP data
- Moving to a more frequent delivery of aluminium sheets
- Can provide a smooth and steady demand for supplier
Give three examples supplys of different types of physical inventory in both categories, “its position” “its purpose” (3)
By position in the value stream
- Raw materials
- WIP
- Finished Goods
By Purpose
- Safety Stock
- Buffer Stock
- Shipping Stock
