116
MANUFACTURABILITY OF HIGH INTEGRITY DIE CASTINGS
Figure 7.2 Diagram of Z-1 fuel rail design.
All data related to complete die fill were collected by visual ex- amination of fuel rails after manufacture. Leakage due to porosity
was detected using air pressure decay methods after machining. Further analysis of porosity was performed by using metallo-
graphic methods. Dimensional stability was determined using co- ordinate measuring machines.
7.3.3 Review of the Z-1 Fuel Rail Design
Figure 7.2 is a diagram of design Z-1. The main features in this design are the fuel inlet A and fuel outlet B tubes, the fuel
injector pockets C, D, E, and F, and the fuel pressure regulator boss G.
The Z-1 design was initially manufactured by forging an alu- minum billet followed by extensive machining. The original
weight of the aluminum forging billet for the Z-1 fuel rail is 1500 g. After forging, the rough fuel rail weighs roughly 800 g and is
then reduced by machining to approximately 500 g. During proc- essing, two-thirds of the weight from the initial aluminum forging
billet is turned into scrap.
As a cost savings effort, production of the rough Z-1 fuel rail was shifted from forging to a high integrity die casting produced
7.3 AUTOMOTIVE FUEL RAIL CASE STUDY REVIEW
117
using the semi-solid metalworking process. This shift was made without redesigning the Z-1 fuel rail. The semi-solid rough part
weighs roughly 550 g as cast and about 400 g after machining. The scrap weight and finished part weight reductions were ob-
tained by the increased net-shape capability of semi-solid metal- working processing over forging.
The Z-1 fuel rail, as stated earlier, was originally designed to be manufactured using the forging process. Initial trials showed
that the Z-1 fuel rail could be manufactured using the semi-solid metalworking process without redesign by using a gate at the cen-
ter of the rail with a large cross section.
Several areas of the Z-1 design, however, were prone to fill problems, including the inlet and outlet tubes features A and B,
respectively in Figure 7.2 and the corners of the regulator boss feature G in Figure 7.2. The tips of the injector pockets features
C, D, E, and F in Figure 7.2 also exhibited filling problems. In order to feed the inlet tube, the metal flow had to turn its direction
about 120⬚. Fill problems such as these were detected by visual examination during production.
Shrinkage often occurred in the large masses found in the Z-1 design. Machining periodically cut into the shrinkage porosity,
creating leak paths. Such issues were detected using air pressure decay methods. The fuel pressure regulator pocket, feature G in
Figure 7.2, was most prone to shrinkage. The micrograph in Fig- ure 7.3 shows shrinkage typical to that found in the fuel pressure
regulator pocket.
The Z-1 fuel rail design is in conflict with many of the design for manufacturability guidelines defined for high integrity die cast-
ing processes, including
1. lack of consistent wall thickness, 2. several large metal masses,
3. sharp transitions between features, and 4. minimal use of fillets and radii.
The draft angle used in the manufacture of the Z-1 design was found to be acceptable.
