NC-designed tooling cuts scrap, improves quality in FPC manifold manufacturing; production tooling can reduce rejects, improve casting quality and lower casting costs.

NC-Designed Tooling Cuts Scrap, Improves Quality in FPC Manifold Manufacturing

Production tooling can reduce rejects, improve casting quality and lower casting costs.

The resources of Teksid (Fiat) and Fataluminium, both of Torino, Italy, were pooled recently to improve the quality of intake and exhaust manifold castings manufactured by the foam pattern casting (FPC) process. Their work revealed that errors made early in the tool design process were costly, causing excessive scrap rates at the two sites producing 5000 castings a day.

The end result of their project was the development of a molding system that significantly reduced production spoilage.

Product engineering established the fact that at least half of the total volume of scrap was due to dimensional inconsistencies already present in the pattern before the sand filling and pouring operations, the kind of flaws normally caused by out-of-dimension tooling or poor molding and the gluing methods.

The main faults found were geometric and/or dimensional errors due to the pattern molding and gluing processes and coating and sand inclusion in the casting due to incomplete sealing of the glued pattern surfaces.

As production volumes rose, these faults were compounded since various tools, mounted on different machines, were used for the same type of casting. Thus, it was virtually impossible to stabilize, much less reduce, the scrap rate; the progress made metallurgically and in the sand filling and pouring phases was offset by the deterioration of the pattern quality.

These faults revealed that there were differences between different sets of the same tooling, providing limited reliability in the molding and pattern gluing machines.

Inevitably, attacking scrap and quality-related problems uncovered a range of causes, making it necessary to work in many directions at once.

Improving Pattern Quality

Patternmaking machines use master models to replicate patterns machined from blocks of alloyed aluminum. Special machinery is also used to make gluing equipment, or a resin-pouring procedure can be used.

The level of accuracy attainable using these methods is not always sufficient to guarantee all the dimensional tolerances desired in the resulting castings. Automotive component designers now require ever more stringent dimensional accuracy, even for rough castings, to reduce the amount of machining required on any given part, its finished weight and the price per piece.

The often enormous difficulties that already affect the construction of single or sample tooling are aggravated when different sets of identical tools have to be used to meet scheduled production volumes. Since the production capacity of pattern-molding and pattern-gluing machines is quite limited (from 40 to 60 cycles per hour, maximum), the need to use multiple tooling extends to more or less all the various types of castings to be produced in medium or high volume.

An accurate statistical analysis of the main causes of faults and their effect on the total amount of scrap carried out on intake manifolds produced with multiple tooling emphasized the important role tooling plays in the dimensional accuracy of the castings. The solution to this kind of close dimensioning problem appears to lie in the design and production of all the tooling using CAD/CAM systems according to the following: * analyze component drawing, define any missing dimensions for mold construction; * establish pattern parting lines; * generate NC programs complete with video simulations; * develop a mathematical model; * validate NC programs, if required; * check on resin; * rough machine aluminum inserts with NC programs and 2 mm (0.08 in.) machining allowances; * rough-machine mold stabilization through treatment at 200C (392F) for 2 1/2 hr; * aluminum insert semifinishing using NC programs and 0.5 mm (0.02 in.) machining allowances; * finishing to be carried out using NC program 0.05 mm (0.002 in.) preset accuracy; * dimensional checks on NC machined tooling on geometric control machines according to mathematical model; * drill polystyrene injectors and air and steam vents on the cavity inserts of the molding equipment; * drill suction holes in the printing side of the gluing tools; * manually finish and polish the molding equipment cavity.

Following these steps, a complete molding and gluing tooling set for an intake manifold was designed using multiple multi-impression equipment.

A comparative analysis was carried out on significant numbers of castings produced using patterns manufactured with two types of tooling. The results consistently confirmed a marked improvement in the production of good castings from parts produced using CAD/CAM-developed tooling.

Considering the results obtained and in order to complete the tests, backups of the CAD/CAM-type tooling were manufactured, gradually replacing the traditional tooling. The result was more uniform polystyrene patterns and eliminating differences between the various sets of tooling.

The experience gained in this project has made it possible to achieve important benefits in higher production and quality, with lower scrap rates and reduced casting costs. In the case of the aluminum intake manifolds, a 3-4% reduction in scrap has been achieved in large volume production.

Alfredo Dal Pan Fataluminium SpA Torino, Italy