发布时间 : 星期二 文章北美压铸压铸件公差标准(NADCA Standard, Brief)更新完毕开始阅读
NADCA Standard
Linear Dimensions: Standard Tolerances
Linear Dimensions: Precision Tolerances
Parting Line: Standard Tolerances
Parting Line Tolerance is the maximum amount of die separation allowed for the end product to meet specified requirements of form, fit and function. This is not to be confused with Parting Line Shift Tolerance which is the maximum amount die halves shift from side to side in relation to one another.
Parting Line Tolerance is a function of the surface area of the die from which material can flow from
one die half to the other. This is also known as Projected Area.
Projected Area is always a plus tolerance since a completely closed die has 0 separation. Excess material and pressure will force the die to open along the parting line plane creating an oversize condition. The excess material will cause the part to be thicker than the ideal specification and that is why Projected Area only has plus tolerance. It is important to understand that Table S-4A-2 (Projected Area Tolerance) does not provide Parting Line Tolerance by itself. Part thickness or depth must be factored in to give a true idea of Parting Line Tolerance. Parting Line Tolerance is a function of part thickness perpendicular to the Projected Area plus the Projected Area Tolerance.
Example: An aluminum die casting has 75 in2 (483.9 cm2) of Projected Area on the parting die plane. From table S-4A-2, Projected Area Tolerance is +0.012. This is combined with the total part thickness tolerance from table S-4A-1 to obtain the Parting Line Tolerance.
The total part thickness including both die halves is 5.00 in. (127 mm) which is measured per-pendicular to the parting die plane (dimension “E2 E1”). From table S-4A-1, the Linear Tolerance is ±0.010 for the first inch and ±0.001 for each of the four additional inches. The Linear Tolerance of ±0.014 inches is combined with the Projected Area Tolerance of +0.012 to yield a Standard Parting Line Tolerance of +0.026/-0.014 in. or in metric terms ±0.35 mm from Linear Tolerance table S-4A-1 plus +0.30 mm from Projected Area Tolerance table S-4A-2 = +0.65/-0.35 mm.
Parting Line Shift: Standard Tolerance Example: Parting Line Shift Tolerance
The cavity area at the parting line is 75 inches squared. From Table S-4A-6, the Projected Area Parting Line Shift Tolerance is ± 0.006 (±0,152 mm). This is added to the Linear Tolerance from table S/P-4A-1.
Draft Requirements: Standard Tolerances
In the case of an inside surface for an aluminum cast part, for which the constant “C” is 30 (6 mm), the recommended Standard Draft at three depths is:
Cored Holes for Cut Threads: Standard Tolerances
Cored holes for cut threads are cast holes that require threads to be cut (tapped) into the metal. The table below provides the dimensional tolerances for diameter, depth and draft for each specified thread type (Unified and Metric Series). When required, cored holes in Al, Mg, Zn and ZA may be tapped without removing draft. This Standard Tolerance recommendation is based on allowing 85% of full thread depth at the bottom D2 (small end) of the cored hole and 55% at the top D1 (large end) of the cored hole. A countersink or radius is also recommended at the top of the cored hole. This provides relief for any displaced material and can also serve to strengthen the core.
Threads extend through the cored hole as by Y. X shows the actual hole depth. As with the countersink at the top of the hole, the extra hole length provides relief for displaced material and allows for full thread engagement. Tolerances below apply to all alloys.
Table S-4A-9: Cored Holes for Cut Threads (Standard Tolerances) – Unified Series and Metric Series