Product Design for Manufacturing
10 Things a Designer Should Know
Part 1

You’re designing a product to be manufactured and you want to be sure all your hard work will not have to be revised before the design is released for production. How do you optimize your design for manufacturing? What are the significant considerations that must be taken into account? This article will provide you with a detailed list of the top ten essential parameters to verify before releasing your manufacturing design.

  1. Clearly define your forecasted production requirements
  2. Specify product cost
  3. Be realistic about your investment
  4. Select the optimum manufacturing processes for your product
  5. Account for assembly time and cost
  6. Design for ease of assembly
  7. Define quality standards
  8. Know your vendor’s capabilities and limitations
  9. Optimize your tolerance requirements for your suppliers
  10. Define special testing and QC requirements

Clearly define your forecasted production requirements

One of the first critical decisions you must make before you begin a design is your selection of manufacturing processes. Process selection is highly dependent on your product requirements and your forecasted sales. The process or processes you select will affect how your product will look, function, cost, and be designed. The definitions of high or low production are relative. High production volumes are unquestionably always cost-effectively manufactured with minimal labor and part costs. Low annual production requirements won’t justify high capital investments that cannot be amortized within any reasonable time period and will be most cost-effectively manufactured with higher labor content and higher part cost. Defining the breakeven point for upfront investments in tooling vs. return on investment (ROI) is simple. The timeframe or your ROI is referred to as the amortization period. The amortization period is determined by simply dividing your total capital investment for a part many parts by the number of products to be sold within a given period of time. For example, if you expect to sell 20,000 units of a product in one year and your allocate $200,000 in molds for plastic parts, your amortized cost per unit is $200,000/20,000 = $10/ unit for the first year. After the first year, the $10/part burden will disappear. If we compare this example to a second scenario where the same investment is made for 200 units in the same timeframe, the amortized cost will be $200,000/200 = $1,000/unit!! Although the second option appears to be cost-prohibitive, it may be required in some circumstances when there are no other options.

Manufacturing processes that are capital intensive include injection molding, die casting, and matched metal die forming. Alternative processes that require less upfront investment include vacuum forming, sheet metal and machining. The materials and design details for all of these processes are unique to each process and will affect all aspects of product appearance, number of parts, design details, assembly features and product performance.

Specify product cost

Define the selling price for your product. Determining the optimum sales price for a product is one of the most critical decisions in its development and eventual introduction. Products must be designed and manufactured to sell at an affordable price that is balanced with their value. If the selling price cannot be justified by its value, the product will fail based on its limited sales. Sales price should be determined based on the following variables:

  • Bill of materials cost
  • Manufactured cost
  • Competition prices
  • Product benefits and value

Manufacturers introducing a product into an existing market must objectively assess their product’s benefits and features versus competitive products on the market. The targeted retail price must account for a profit as well as offer more value to the prospective buyer than competitive products. For example, if the selling price of a new product is 50% higher than all the competitive products on the market, it must also offer improved performance, quality, or prestige than the competition to be successful. An alternative strategy would be introducing a very low-cost product with limited features and high quality.

Regardless of the business strategy, the manufacturing costs must provide enough margin to the targeted selling price to allow for a reasonable profit. Some products in highly saturated markets will require high initial capital investments to minimize reoccurring per unit cost versus new highly innovative products with less competition. In all cases, business planners must always focus on product value. As value decreases, so do the chances of a successful product.

The initial capital investment and the targeted unit price will directly impact design. High sales volume products that are priced within narrow profit margins must be designed with minimum labor, part count, and very efficient assembly times. Conversely, products sold in lower production quantities at higher prices may warrant lower capital investments, higher part count, and higher labor content.

Be realistic about your investment

Inventors, startups, and established companies often ignore understanding the significance of investments in capital equipment, including molds, machinery, and fixtures. The investment in molds for plastic parts can often be costly, usually ranging from $50,000 to as much as $1,000,000, depending on the product. You must be willing to risk your own money or find investors who will provide you with the appropriate funds to the molds. If neither of these options is available, you must abandon your plans or revise them to lower the investment. Changes to your investment plan will drastically affect the overall design, unit cost, and marketing strategy. It’s therefore always wise to confront these difficult decisions at the beginning of a project before time and money are wasted in design and development.

Select the optimum manufacturing processes for your product

After the three previous considerations have been taken into account and decided upon, the next major decision is selecting the optimum manufacturing process or processes. Production designs are wholly dependent upon the material and manufacturing process. For example, products designed for sheet metal must be specifically designed for that process. They will look and function very differently from the same product designed for injection molded thermoplastic. The investments for a sheet metal product are virtually nothing compared to an injection molded part. Many manufacturing processes have advantages and disadvantages, depending upon the application, material, budget, and investment. Below is a list of manufacturing options for plastics and metals:

Plastics

  • Injection molding +5 to 10 variations of this process
  • Blow molding – extrusion blow molding & injection blow molding
  • Thermoforming – vacuum forming, pressure forming & twin sheet forming
  • Rotational molding
  • Extrusion – profile extrusion, co-extrusion, sheet
  • Compression molding
  • Casting
  • 3D printing – many options
  • Machining

Metals

  • Sheet metal
  • Matched metal stamping
  • Forging
  • Investment casting
  • Die casting
  • Machining
  • Plaster casting
  • Sand casting
  • Roll forming

Product designs will vary according to each of the processes listed above. Designers must be aware of the materials, processing parameters, secondary operations, and design limitations for each of the aforementioned techniques to design a product for manufacturing properly. A lack of understanding will often lead to costly tooling revisions, production delays, expensive parts or poor quality.

Process selection should be based on all the previously cited criteria and the application and market requirements.

Account for assembly time and cost

Product design features and the number of parts will influence assembly time and cost. Product designers and design engineers constantly balance the trade-offs between capital investment, part count, and labor. Although designers always try to minimize the number of parts and labor, they are simultaneously faced with opposing requirements such as reducing capital investment and optimizing ease of serviceability. Parts consolidation is often achieved by designing more complex multifunctional parts which require higher capital investments. These more significant, difficult parts are often more challenging to disassemble during service calls. Elimination of hardware by incorporating snap fits and molded-in features reduces part count and labor but typically increases tooling investment.

Designers must continuously evaluate the dynamic cost trade-offs between these parameters throughout the design and development process. Product designers should make these critical decisions based on feedback from manufacturing, marketing, sales, and service department officials. For example, a product may require 80 assembly steps during a 30-minute total assembly cycle based on a capital investment of $100,000. The assembly time could be reduced to 18 mins, if an additional $35,000 was invested, reducing the assembly process to 45 steps. The reduction in time would reduce total unit cost by 15%. Is the added investment warranted? The answer to this question depends on one or more of the parameters listed below:

  • Does the added investment reduce unit cost, making the product more cost-competitive increasing the chances of a more significant market share?
  • What is the risk of achieving the added market share?
  • How much cost savings is required to achieve that goal?
  • When can the added investment be fully amortized, one year, two years, or more?
  • Will the design modifications make serviceability more difficult and time-consuming?
  • Will the design modifications adversely affect product appearance or decrease quality?

You can readily appreciate the number of critical parameters that can influence your decision. In most situations, the decision-making process is typically limited to a few key factors, and the matrix of variables is relatively straightforward.

The second portion of this two-part series will focus on the remaining factors that should be considered when designing a product for manufacturing.