Capturing the geometry of an existing part can play a critical role if this data can successfully be used for a FEM or process analysis. The computer modeling and analysis method can the be applied to assist in the manufacturing process. A 3D electronic format of the part is required to perform an analysis or process modeling of a manufacturing process. 3D CAD and STL files existed, but these files proved to be unacceptable for FEM analysis. The STL file was generated from the 3D CAD file. A new STL file generated from the CAT scanning data may solve the problem.
 
 

4.11.1 Background
 
 

The quarter scale SLA prototype was CAT scanned using the GE. CAT scanner at Hydromed Hospital based in Bloemfontein. The 2D CAT slices were again stored on 4mm DAT magnetic tape. 2D CAT images of various positions were stored on film for record.
 
 

4.11.2 Conclusion
 
 

2D CAT images were checked during scanning. The window settings were optimized on the CT computer. It is again clear that the material what the part is made of plays a major role. The SLA prototype in made of an epoxy polyester. Measurements were taken of the part’s wall thickness and compared to measurements taken from the CAT scan images. In general, the CAT scan images proved to be 0.4 to 2mm thinner than the actual part. Again, the threshold was set to the optimum. Clearly, the SLA material was not suitable to CAT scanning. Referring to an earlier section (3.6), material’s density and atomic number are important factors to obtain an acceptable CAT scan image. A lot of detail was lost at the thinner wall sections and can be seen from the generated 3D images. Due to the material, the process could not be fully evaluated.

4.12.2.1. Images
 
 
 

Figure 4.11.2  3D Reconstructed Gearbox housing.	Figure 4.11.2  3D Reconstructed Gearbox housing.
Figure 4.11.2  3D Reconstructed Gearbox housing.

 

4.11.3 Gearbox Housing Data Sheet:
 
 
 

	Description	Options (Default)	Data
1	CT Image Names		1s6I.*
2	Patient/Project Name		1s6I
3	Number of First Input Image		E6281S6I1.CT
4	Number of Last Input Image		E6281S6I79.CT
5	Number of First Output Image		1S6I1_1.000
6	CT or MRI	CT, MRI	CT
7	Horisontal Nr. Of Image Pixels	0 to 65535 (265,512,1024)	512
8	Vertical Nr. Of Image Pixels	0 to 65535 (265,512,1024)	512
9	Number of Images per File	(1)	1
10	File Swap Format (0,3)	0,3	CCGEADVA
11	Pixel Type	B,UB,S,US,L,UL,F	-
12	Header Size	*see formula below	-
13	Inter Image Header Size	0	-
14	Add Value	0 to 4095	-
15	Scale Value	0 to 4095	-
16	Table Position	(mm)	0
17	Distance Between Slices	(mm)	1
18	Slice thickness	(mm)	1
19	Pixel Size SQ.	F.O.R./Nr. Hor. Pixels (mm)	0.47
20	Gantry Tilt Angle	Degrees	0
21	Field of Reconstruction/View	(mm)	240
22	Number of Images		79
23	File Size of CAT Image	kb	270-280
24	File Size of Converted Image	kb	11-23
25	.3dd file size	Mb	3.2 *.srf
26	.STL file size	Mb	17
27	RP Method	(SLA,FDM,OTHER)	SLA
28	.IGS file size	Mb	-
29	RP Slice file size	Mb	19
30	RP Download File size	Mb	16
31	Grow Time	Hour	6
32	Tip size	(T12, T25)	-
33	Slice Thickness	(0.01", 0.014")	0.01"
34	Finishing Time	Hour	3
35	Processing Time	Hour	2
36	Data Retrieval Time	Hour	2
37	Total Cost	Rand	=8*250=2000