Dfa Analysis - Vhs Cassette Assembly

1.4 Assignment Objective

The objective of this assignment (first part) is to perform design for assembly (DFA) analysis on an artefact that is commercially available and existing. The artefact chosen is a typical VHS cassette tape, which is been in the market for more than two decades. DFA analysis is to be conducted on this part considering a manual assembly sequence with the individual parts and sub-assemblies identified.

During the analysis, a detail time study is to be performed on the individual parts assembly and sub-assembly to arrive at the total assembly time and stations. The results of the analysis are to be evaluated and various design modifications need to recommended so as to improve the DFA efficiency leading to the overall cost reduction of the product.

1.5 Assignment Approach

The following step-by-step approach is adopted for achieving the objective of this assignment (first part).

Step-1. The VHS tape is carefully disassembled and individual components are identified and a bill of material is created.

Step-2. A clear understanding of the functionality and design criteria on each of the part is determined and charted out.

Step-3. Various ways of assembling the product is tried out and an ideal assembly sequence is arrived at keeping the least cycle time for assembly.

Step-4. Manual assembly layout is worked out and a balanced line is achieved using the largest candidate rule.

Step-5. DFA analysis is performed on the artefact using the Lucas method and the results are evaluated.

Step-6. Alternate design suggestions and improvements are thought of in order to improve the DFA efficiency and for reducing the over all assembly cycle time.

Step-7. The artefact is re-evaluated with the improved design and DFA analysis is performed until the highest possible DFA efficiency is achieved.

Step-8 Advantages and cost benefits of the improved design is examined and suggested.

Chapter 2: Description of the Artefact

2.1 Construction and History

The artefact selected for this exercise is a VHS cassette (Fig. 2.1). This product needs to be manufactured in high volumes, as the demands are usually high. The product has about 20 individual parts assembled. Most of the parts are made of plastic material except for the steel rollers, springs and screws. It basically consists of magnetic tape wound between two spools and various rollers make up the path of the tape. It has several features such as the self-aligning centres of spool rotation, tape spool rotation interlock, spool viewing window, tape protector, spool bias force, tapered spline coupling for spool drives, etc.

Figure 2. 1 VHS Cassette

2.2 VHS Cassette- Exploded View

Figure 2. 2 Exploded view of the VHS Cassette

2.3 Bill of Material

Table 2. 1 Bill of Material

Part # Description Qty Material Type

1 Cassette Base 1 No. Plastic MFG

2 Tape Protector Interlock 1 No. Plastic MFG

3 Tape Protector Interlock Spring 1 No. Spring Steel STD

4 Tape Guide Roller 1 No. Plastic MFG

5 & 6 Tape Guide Pin (Hollow) 2 Nos. Stainless Steel STD

7 Tape Guide Plastic Film 1 No. Plastic MFG

8 Tape Guide Pin Steel 1 No. Stainless Steel STD

9 Spool Rotation Interlock Release 1 No. Plastic MFG

10 Spool Release Left 1 No. Plastic MFG

11 Spool Release Right 1 No. Plastic MFG

12 Spool Release Spring 2 Nos. Spring Steel STD

13 Tape Spools 2 Nos. Plastic MFG

14 & 15 Tape Indicator Windows 2 Nos. Plastic MFG

16 Spool Bias Spring 1 No. Spring Steel STD

17 Cassette Top 1 No. Plastic MFG

18 Tape Protector Spring 1 No. Spring Steel STD

19 Tape Protector 1 No. Plastic MFG

20 Screws 5 Nos. Steel STD

2.4 Part Function Criteria

Part #: 01 Qty: 1 no.

Description: Cassette Base

Material: Plastic

Function:

The cassette Base forms the housing onto which most of the other components are assembled. The concept of having a single base component makes the design more efficient for assembly. Necessary provisions are made on the base component to aid the fitment for all the other parts.

Part #: 02 Qty: 1 no.

Description: Tape Protector Interlock

Material: Plastic

Function:

This part provides an interlock for the tape protector such that it does not allow the tape protector to open up when the cassette is out of the VCR machine. Only when the tab on the tape protector interlock is pressed, the tape protector opens up freely. The design of this part takes care of the automatic reset when the tape protector returns to the closed position

Part #: 03 Qty: 1 no.

Description: Tape Protector Interlock Spring

Material: Spring Steel

Function:

The function of this part is to aid the automatic return of the tape protector when it is released. This part keeps the tape protector normally