Process Selection for a Manifold Jacket

Introduction

In this case study processes are sought to make a small batch of manifold jackets for use in a space vehicle, as shown in Figure 1. The manifold is to be made of nickel. It is large, with a mass of about 7 kg, and has a complex 3D-hollow shape. The minimum section thickness is 2-5 mm. The requirement on precision is strict (precision < 0.1 mm). Because of its limited application, only 10 units are to be made. Table 1 lists the requirements.

Figure 1 Manifold Jacket for use in a space vehicle, from [2]

Design Requirements

Material Class	Non-ferrous metal
Process Class	Primary, Discrete
Shape Class	3D-hollow-transverse features
Mass	7 kg
Minimum Section	2-5 mm
Precision	0.1 mm
Batch Size	10

Table 1 Manifold Jacket: design requirements

 

The Selection

Figure 2 shows the first selection stage: a bar chart of mass range against material class, choosing 'non-ferrous metal' from the material class menu. The selection box is placed at a mass in the range 5-10 kg. Many processes pass this stage, though, of course, all those which cannot deal with non-ferrous metals have been eliminated by the choice of material class.

Figure 2 A chart of mass range against material class. The box isolates processes which can shape non-ferrous alloys and can handle the desired mass range

We next seek the subset of processes which can produce 3D-hollow shapes with transverse features and the desired section thickness. '3D-hollow-transverse features' is selected as the shape class on the x-axis and section range is chosen as the y-axis in Figure 3. The selection box specifies the requirement of a section thickness in the range 2-5 mm. Again, many processes pass. Those which cannot produce the desired shape and thickness range fail.

Figure 3 A chart of section thickness range against shape class. The chart identifies processes capable of making 3D-hollow shapes having transverse features with sections in the range 2—5 mm

The next selection stage, shown in Figure 4, is a bar chart of tolerance against process class, selecting 'primary' from the process class menu, meaning that it we require a 'forming process', not a 'joining' or 'finishing' process. The selection box specifies the tolerance requirement of 0.1 mm or better. Very few processes can achieve this precision.

Figure 4 A chart of tolerance against process class. The box isolates primary processes which are capable of tolerance levels of 0.1 mm or better

The last selection stage considers economics (Figure 5). A batch size of 10 units is desired. The selection box isolates the processes which would be economic for such a small batch size. The processes which passed all the selection stages are labelled.

Figure 5 A chart of economic batch size against process class. Three processes have passed all the stages. The selection box isolates the processes which are economic for making 10 units

 

Results

Processes Passing All Stages
Manual Investment Casting
Electroforming

The strict requirement on tolerance caused many processes to fail. The cost consideration suggests that the most suitable processes for making a batch size of 10 manifolds, which satisfy all of the other requirements, are manual investment casting or electroforming. The small number of units required, for such a limited application as a space shuttle, does not justify the investment in more expensive automated processes.