Ganesh Iyer is Managing Director at SSA Techknowlogies Pvt Ltd. SSA Techknowlogies provides Design Excellence Consulting, using methodologies for New Product Introduction Process by Product Cost Reduction and Warranty Costs

Reduction. These solutions use Lean Manufacturing, Design For Six Sigma, Quality Function Deployment (QFD), TRIZ- Theory of Inventive problem solving, Design for Manufacture & Assembly (DFMA), Design Failure Modes Effect Analysis (DFMEA), Advanced Product Quality Planning (APQP) etc. SSA Techknowlogies focuses on ‘Quality in Design’ through developing designer’s skill, improving product introduction process (PIP), reducing development lead times, improving product quality and reliability, and thus improving profitability.

Nilesh Nevrekar is a Project Manager at Polysmart Technologies Pvt Ltd. Polysmart Technologies Pvt. Ltd. is Silver certified Moldflow Consulting Partner offering engineering services focused on plastic products. Polysmart provides solutions to convert metal components to plastics by redesigning to optimize

number of components and improving the functionalities. Polysmart follows the Six Sigma methodology and provide engineering design consultancy services in the areas of concept design, product engineering & detailing, meshing, structural analysis, Moldflow analysis, value engineering studies, Rapid prototype, mould design & audit and soft tooling. Overview of Robust Design Process

Plastic products are widely used in our day to day life. It is widely applied and used in many areas and is actively replacing its metal counterparts. However product quality of plastic products is inconsistent and there exists a variation among similar products. The variation is quite significant in conventional plastic injection molding process.

Companies with traditional quality activities make sure their products are of highest standard by inspecting the parts produced at the end of the production line and it is a common process in all Indian companies. Also, the attributes of the products were established by engineers, who backed with years of experience, established parameters based on subjective trials. However, to create stability in the quality of the product and to increase market competitiveness was imperative. So a new approach was essential

The concept of Robust Design Process challenges our tradition of inspection and asks the question, can the product be made right the very first time, with confidence? Experience has shown that quality improvement efforts are more successful when done in activities before production.

One of the very early Gurus who proposed the idea that Quality should be designed into the product and not inspected is Dr. Genichi Taguchi. He also proposed that the product quality

should not be influenced by uncontrollable noise factors (environmental variation during the product usage, manufacturing variation and component deterioration). Traditional quality has a concept of end user specification limits, and for all designers & quality community, if we are within specification, then quality is met; however Tachuchi proposed that anytime, we deviate from the set target, loss to customer satisfaction and warranty costs increase.

Figure 1, depicts the concept of robust design. When we plot the graph of output desired parameters with input or process parameters, a robust design is one where the output is not significantly influenced by changes in the input or process parameters.

In the design of plastic parts specially, major emphasis is on cost, aesthetic appeal, functionality and lastly manufacturability. Designers work within these constraints and usually trade-off one or the other aspect, which leads to premature failures. The robust

design process starts with Market & Customer Research, i.e. study of existing customer requirements, competitor products, and then list down the data of SWOT Analysis to know where our product idea stands in the market. One of the Powerful tools developed by SSA to implement in the initial stages is called ‘VOC Benchmarking’ in addition to the usual product and or process benchmarking.

Then the next step is to do the Concept Design based on the gathered data & come up with different concept models. The different concepts are then converted into physical prototypes to get a feel of the product & market feedback is gathered & the concept design is frozen. Once the concept design is frozen, detailed engineering is carried out with respect to structural as well as functional point of view.

Some of the more common failure causes in plastics is related to sharp corners, wall thickness, creep stress, environmental impacts, and position of ribs. Some of the attributes to consider during design are type of material, load, duration and temperature. In the next stage of Product Design Validation, some of these factors are validated during the design stages using structural analysis

tools like finite element analysis (FEA) and Part & Process Simulation using Moldflow®. These advanced techniques provide early indication of the weak areas, foretell the molding problems in the part & take corrective action in the design phase itself to save rework cost on the tool as well as can avoid delays in the project.

Figure  1:  Robust  Design

Once analyzed the next important step is that of Prototyping to generate the physical model that provides the size, shape, feel and function of the component to provide a higher degree of interaction between members of product design team. In past people used to make scaled down clay models to get actual feel of the part, but new technology like SLA, SLS, FDM, 3D printing have replaced the old conventional Methods which doesn't only give precise results but also save man hours

and time.

Reliability testing of the product is yet another aspect often ignored since plastic parts deform over time with sustained load. In this regard, with monitoring and controlling the dimensional tolerance variation is essential. In this area, the six sigma techniques really help to reduce variation during the production runs and also identify and fix the root causes of the problems

Statistical process control is a method of quality control, which uses statistical techniques. After the part is approved we need to control & sustain the same quality over a period of time during production. This is one of the tools to measure the process capability.

Today, a new methodology called Scientific Injection Molding (SIM) is available which is a powerful tool for process optimization. SIM is a scientific approach for establishing the processing variables. The ultimate objective of SIM is to achieve a robust molding process. It deals with identifying the keys areas of individual processes

& its sub-processes. By following this approach we can control individual phases like Filling, packing, cooling etc which makes it a close loop system & also identify easily where the problem lies in comparison with the old conventional molding process.

The systematic stage gate design and development process considers all these aspects and invariably comprising on some of these steps, leads to significant rework and customer dissatisfaction later.

While all this seems to be a lot of activities, industry leaders have practised these offerings and techniques for long. In an attempt to look at how to better the workflow in all these various stages, Lean is applied in NPI (New Product Introduction process) to improve the delivery time of new products and introduce these best practices at appropriate stages. Just like as Lean is applied in Manufacturing to eliminate waste and create flow, Lean is applied in Design and development using SSA’s NPI Lean approach that follows the RMAOR® (Recognise, Map & Measure, Analyse, Optimise, Repeat) methodology.

NPI Lean process for Plastics Design and Development

The suggested robust design process must cover the following high level steps:

Case Study for Robust Design Process as implemented in Polysmart:

Project Brief:

• Product is used in the assembly of the water treatment system. At first the component was developed in metal. The product cost was too high

• The component should withstand the continuous operating pressure of 100 psi & it should pass all the product approval procedures like leakage test, bursting test, etc

• A challenging task to convert the thick walled component (thickness: 8mm) into plastics & that to which needs to be manufactured by injection molding process

Objective:

Metal to plastics substitution of the product & to make it feasible to mold with the injection molding process

Product Re-Engineering using Moldflow & Structural Analysis software

Plastic Product Design validation to match the customer’s requirement

Process monitoring to ensure consistency in the quality of the part

Approach:

Component Location:

Material Selection Criteria:

The component should withstand the pressure of 100psi It should qualify for the bursting pressure as per the product requirements given by the

customer The component is used in water application hence the plastic material

should have lower water absorption with good dimensional stability The component will be in contact with water, so the material grade should

comply to the FDA & ROHS regulations (i.e. material grade should be NSF approved & it restrict the use of lead, cadmium, mercury, etc)

It should be light in weight

Material Details:

PA-12, 43% glass reinforced. NSF 61listing in several colors. FDA compliance. Low water absorption. Hydrolytic stability. Dimensional stability. Suitable for fluid engineering applications including pump housing, pump impellers & water meter components

Product Optimization:

DFM Study:

Moldflow Analysis:

FEA Analysis:

Mold Design:

Mold Manufacturing:

Part Manufacturing:

Process Monitoring:

An issue arised on Sink marks and Porosity

Cause and Effect Diagram was created to understand the root cause:

Design of Experiments (Shop Floor):

Statistical Process Control (SPC) to ensure Quality of the part:

Conclusion

• Product was re-engineered with respect to plastic product design guidelines • Product Design was optimized by combining two different parts to

form one single part, leading to cost saving in Material, Manufacturing cost & Assembly processes without affecting the end application

• The longer cycle time was addressed by cooling the 90% of the part in mould & remaining outside the mould by putting part in water bath to save on the cycle time & increase productivity

• By applying various methodology of Six Sigma, FEA & Moldflow we were able to solve the chronic issue of porosity & sink marks which was affecting the quality of the part

• Process Capability Study was used to precisely monitor the consistency in the quality of the part