Season 4 Challenges

REWARD - INR 3,00,000
Ferous Oxide

Customers prefer watches made from metallic plated plastic case for several reasons such as improved aesthetic values, reflectivity and abrasion resistance. In addition, the advantage of use of metalized plastic components, instead of metallic parts itself, is the light weight construction and higher corrosion resistance. To impart aesthetic values and mechanical strength, plastic parts of the watches are coated with metal via a process called physical vapor deposition (PVD) or electroplating. Electroplating is one of the widely followed techniques in Automotive industry due to its cost-effectiveness and ability to handle larger volume of materials for plating. We intent to do this metallic coating on plastic components of watch with a lower batch size of up to 500 units. Moreover, the process led by electroplating is subject to the requirements of the regulation and is likely to be banned due to toxic issues concerned with the technology. Hence, we wish to use PVD technique as an alternative to impart metallic coating on plastic components, using vacuum thermal evaporator. The metallization of plastic components is achieved via the principle of 2-layer coating namely 1) base coat (to impart adhesion) and 2) metal coat (to impart aesthetic appearance). At present, there are no commercially viable PVD techniques available in India, considering the batch size of 500 watch units, for coating metal layers on plastic substrates. In our case, the work pertain to metallization of plastic components is accomplished using external facility. However, at times, due to unrealistic change in vacuum and temperature level, the coating process results in discoloration, bubble and poor adhesion. Consequently, the quality of the metal plated plastic components gets affected which eventually leads to rejections of parts which is as high as 10%. Therefore, we aspire to develop a suitable cost-effective and environmental-friendly solution to eliminate surface defects and in-turn the rejections, as low as possible.

  • Options tried to solve before:
  1. Explored electro plating and vacuum metallization.
  • Future State:
  1. Cost effective/reliable process for plating on plastic - watch case/bezel ring/Decorative ring.
  2. Feasibility of masking on slender parts.
  3. Lower MOQ – 100 to 500.
  • Constraints:
  1. High visual appeal requirements like free from defects, color fading, dent, bubbles and scratches.
  2. Higher quality requirement of aesthetic & reliability.
  3. Difficulty in fixing of crystal (plastic) and watch case (metallized) using ultrasonic welding after metallization due to prevailing of metal-plastic interface at the juncture. To overcome this and facilitate welding, fixture is used to mask the juncture to avoid metallic coating and retain the plastic surface. However, the design of fixtures for different geometries of watch case is complex and requires additional investment (Each model of watches need new fixtures for metallization). Fig. 1 displays the exploded view of various parts of watch case and crystal assembly.
  4. Various shapes/sizes of components.
  5. Difficulty in qualifying the following reliability tests with the plated plastic components:
  • Salt spray test.
  • UV test.
  • Grid Test.
  • Impact Strength test.
  • Wear Test (Standards followed in Automobile industry).
  • Success criteria:
  1. Yield >98%.
  2. Cost effective solution for small batch qty.

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