One of the most common discussions I have with prospective purchasers or designers has to do with the surface cosmetics and what the expectation is for the appearance of the gate inlets as finished. If the part is a highly cosmetic part then it is probable that the as cast/die trimmed gate will not be acceptable and will need to be sanded or removed for esthetics. The added operation will of course add cost so that must be addressed during the quote process so the customer knows what to expect long term.
Many purchasers are not aware what a gate inlet will look like after a die trim to remove the inlets. The aluminum die cast process is not like the plastic mold process where our gate inlets look like pin points and not noticeable. I have included a picture of a typical gate inlet as die trimmed and the same one after a sanding operation. Of course the sanded inlet looks better cosmetically but there is a price to pay for this surface finish which sometimes is required as a preparation for a final coating.
Besides gate inlets the following is a discussion on other metal flash that occurs on most aluminum die castings:
Metal Extension (Flash) Formation and Location
A seam of metal extension may also be formed where separate die parts cast a part feature. Residual metal extension is also formed by the normal operation of ejector pins and will be discussed on an upcoming blog just for ejector pins.
Simplifying Extension (Flash)
Removal Necessary casting metal extension removal costs can be reduced by consideration, in the design stages, of the amount of metal extension to be removed and the removal method to be employed.
Early consultation with the die caster can often result in production economies in the treatment of metal extension removal.
Guidelines to Extent of Removal
The table below provides a guide to the types of die casting metal extension (flash) which occurs in typical die castings and the amount of metal extension material which remains after (1) degating (removal of any gates and runners from the casting), and (2) commercial trimming of die casting metal extension.
Note that in some instances, where special surface finish characteristics are not involved, the most economic method of degating and metal extension (flash) removal may include a tumbling or vibratory deburring operation.
|Guide to Nominal Metal Remaining by Type of Extension|
|Type of Metal Extension and Nominal Amount Remaining After Degating and Trimming|
|Operation Description||Thick Gates & Overflows > 0.12” (3.0 mm)||Thin Gates & Overflows < 0.12” (3.0 mm)||Parting Line and Seam Line Metal Extension||Metal Extension in Cored Holes||Sharp Corners|
|After Degating (Nominal Flash Remaining)||Rough within 0.12” (3.0 mm)||Rough within 0.12” (3.0 mm)||Excess Only Broken Off||Not Removed||Not Removed|
|After CommercialTrimming (Nominal Extension Remaining)||Within 0.06” (1.59 mm)||Within 0.03” (0.8 mm)||Within 0.015” (0.38 mm)||Removed within 0.010” (0.25 mm)||Not Removed|
|* “Commercially trimmed” does not include additional operations to remove loose material. For very heavy gates and overflows, consult your die caster.|
Hopefully after reading the above you will have a better sense of what is involved in preparing an aluminum die casting for the end product use that you require.
As previously mentioned, it is necessary to have dialogue with your die caster at the beginning of the design phase or at least during the quote process. Any die caster that offers value will do a preliminary review of your print and any end use functions and ask pertinent questions so that the quotation will reflect the final part cost.
I have heard many times of a part being awarded to the “low cost” die caster only for the purchaser to find out after the tool is placed that other operations will be needed at more cost.
At Premier we try to educate and work with the marketplace to provide castings at the best possible cost with fewest operations based on an analysis of part prints, specifications, and final end use of the part.
If you have any products that you are considering as an aluminum die casting please send you files and part prints to firstname.lastname@example.org for a free analysis and quotation.
By Leonard Cordaro, President of Premier Engineered Products