Discover Our Insightful Blogs on  Aluminum Die Casting

• Dimensional tolerances depend on part configuration. They are dependent on moving die members, the size of the part (projected area), and whether dimensions run across the parting line of the die. Never specify dimensional tolerances closer than are essential and practical to the die cast process.
• When dimensioning part always specify
  A. Amount of draft.

  B. Where dimension is to be held (does dimension increase or decrease because of draft)
• Provide the maximum permissible radii on all corners and try to stay away from sharp corners wherever possible.
• Keep wall sections a uniform thickness.
• Raised engraving on part is desirable and less costly than depressed lettering.
• Minimum machine stock is very important. Over .030 per side could result in opening up porosity.
• Stay away from holes smaller than 4-40 for the following reasons:
  A. Cannot core.

  B. Porosity is a problem in dig drilling and tapping holes this size or smaller. (Minimum hole diameter as a rule is .125 for aluminum and .093 for zinc.)
• Allow a minimum of three (3) times the pitch of thread beyond depth of required tapped hole depth, to allow for tap lead.
• Stay away from undercuts at base of thread.
• Cast threads are possible in class 1 gage limits, allow a flat at 180° if possible for trimming.
• Use roll taps where possible on depth holes. In the case where a thru hole requires a stronger thread, use a roll tap, but hole should have a cast countersink at both ends to prevent bulge.
• Use heli-coils where excessive assembly and disassembly of bolts is required.
• Utilize cast-in inserts for extreme wear areas.
• Close tolerance machined castings should be stress relieved.

FILLETS

• Intersecting surfaces forming junctions of metal thickness are properly joined with fillets in order to avoid high stress concentrations in the die castings and to control and facilitate maintenance of otherwise squared edges in the casting die. Fillets projected in a direction normal to the parting plane require draft, but the amount is always governed by the draft of the intersecting surfaces. Draft in corners or fillets projecting in a direction normal to the parting plane have approximately 1.5 the amount of draft of the intersecting walls.
• In the sketches above, consideration has been given to the stresses of use and to the stress induced in the die castings of moderate depth. Shallow die castings may have much smaller fillets, while deep pockets and other inside corners may have larger fillets. Sharply squared corners of much length projecting in a direction normal to the parting plane may cause spalled edges in withdrawing the die castings from the die.

RIBS

• Ribs are used to increase the stiffness of, or add strength to, a die casting and to aid in making sound die castings. Ribs are something misused and can be a detriment if working stresses are concentrated by their use or if stresses at the edges of the ribs are high.

EXTERNAL CORNERS

• Sharply squared corners may be used in many locations if die construction permits. This type of corner is often mandatory at parting line locations and die block intersections. Other than this, corners of die castings should have radii in order to prevent early die failure, to reduce the probability of nicking the edge of the die casting in handling, and to minimize material handling hazards for personnel.

• Most die castings can be cast pressure tight. However, in some cases impregnation may be required. Consultation with the die caster in the early design stage is recommended where a requirement for pressure tightness exists in order to take advantage of the basic knowledge of the design and processing factors which will help him to cast pressure tight die casting.
• Important considerations relating to the economic production of pressure tight die casting include the following :

DESIGN

• Successful casting of pressure tight die castings requires conformance to the principles of good die casting design.
• Recommendations concerning fillets, ribs and corners contained in ADCI Product Standard E15 should be followed very carefully.
• Sections should be as uniform as possible.
• Holes and passage requiring pressure tightness should be cored to reduce the effect of porosity. Ample draft should be allowed in cored holes and passages which are not machined.
• Heavy sections should be avoided.
• Careful consideration of the factors of good design will aid in the economical casting of pressure tight die castings.

MACHINING

• The nature of the die casting process is such that the outer surface of a die casting is usually dense and relatively free from porosity.
• A minimum amount of machining stock should be allowed to avoid cutting deeply into a die casting where porosity may be present.
• Avoid large draft angles which would require the removal of a large amount of stock from surfaces to be machined, particularly where holes are cored.
• Where a large amount of machining must be done, impregnation probably will be required after machining.

SIZE

• Larger die castings are generally more difficult to cast pressure tight and will require pressure testing by the caster to assure adequate process control. Impregnation is more generally required for large die castings.

PRESSURE

• Pressure requirements for die castings are generally in order of 5 to 15 psi. Pressure in excess of 100 psi will require special consideration by the die caster.

ALLOY

• Certain alloys are better for making pressure tight die castings. Reference is made to ADCI Product Standard M4 for aluminum alloys (in which comparisons are shown for pressure tightness of various aluminum alloys) to aid in the selection of the favorable alloy.

PRESSURE TESTING

• Reference is made to the last two paragraphs of ADCI Product Standard C8-56.

General Purpose of Standard on As Cast Surface Finish:

• For some applications it is desirable to specify Surface finish requirements. The purpose of this specification is to classify as cast surface finish of die castings into a series of grades so that the type of finish required may be defined in advance. These standards should be used to classify the type of finish only, and final quality. standards should be agreed upon between the die caster and the customer.

• Selection of an aluminum allow for die casting required evaluation not only of physical properties, constants, and chemical composition of the alloy, but also of its inherent characteristics and their effect on production of the die casting and in finishing.
• The table includes certain casting and other outstanding characteristics which are usually considered in selecting a die casting alloy for a specific application. The characteristics are rated from (1) to (5), (1) being the best and (5) being the least desirable alloy. In applying these ratings, it should be noted that all the alloys have sufficiently good characteristics to be accepted by users and producers of die castings. Hence a rating of (5) indicates a commercial alloy, although in certain cases its application may be limited or its manufacture may be restricted to relatively simple die castings.

		Die Casting Characteristics						Other Characteristics (k)
Standard
13, A13	1065 - 1080	1	1	1	1	2	4	5	3	5	3	3
380, A380	1000 - 1100	2	2	2	1	4	3	3	1	3	4	3
Special
43	1065 - 1170	3	3	4	4	2	5	4	2	2	2	5
218	995 - 1150	5	5	5	5	1	1	1	5	1	1	4
360, A360	1035 - 1105	1	2	3	2	2	3	3	2	3	3	1
383	960 - 1080	1	2	1	2	3	2	3	1	3	4	2
384	960 - 1080	2	2	1	2	5	3	5	2	4	5	2

• Ability of alloy to withstand stresses from contraction while cooling through hot- short or brittle temperature range.
• Ability of molten alloy to flow readily in die and fill thin sections.
• Ability of molten alloy to flow without sticking to the die surfaces. Ratings given for antisoldering are based on nominal iron compositions of approximately 1%.
• Based on resistance of alloy in standard type salt spray test.
• Composite rating based on ease of cutting, chip characteristics, quality of finish, and tool life.
• Composite rating based on ease of polishing and quality of finish provided by typical polishing procedure.
• Ability of the die casting to take and hold an electroplate applied by present standard methods.
• Rated on lightness of color, brightness, and uniformity of clear anodized coating applied in sulphuric acid electrolyte. Generally aluminum die castings are unsuitable for light color anodizing where pleasing apperances is required.
• Rated on combined resistance of coating and base alloy to corrosion.
• Rating based on tensile and yield strengths at temperatures up to 500 F (260), after prolonged heating at testing temperature.
• Die casting are not usually solution heat treated. Low temperature aging treatments may be used for stress relief or dimensional stability.
• Die castings are not generally gas or arc welded or brazed.

Note – These data should be used in connection with ADCI-M2 and M3 in determining selection of an aluminum alloy die casting.