Designing an assembly line can be exciting. For in-house manufacturing engineers, it’s a chance to shape the future of your company by designing the physical space that makes your future business possible. For consulting or third-party manufacturing engineers, it’s a way to demonstrate your skills in an interesting new environment. In either case, designing an assembly line is an intellectual challenge that is best conquered with a methodical approach.
Assembly lines are designed for one reason: to make a product. Anything less is unacceptable; anything more is unnecessary. Maintaining this tight focus through design and implementation allows engineers to create the most efficient and effective layout possible. At each stage of assembly line design, engineers must repeat the same question: “what is the simplest way to accomplish my goal?” As you go through the process, here are some factors to consider.
Planning Processes and Material Flow
The most important stage is planning. A simple, efficient plan will carry you smoothly through the installation and operational phases of assembly. Conversely, mistakes made in the planning stage will persist and worsen over the lifetime of the assembly line. Fixing mistakes once the assembly line is built and running will be costly and time-consuming. That said, it’s difficult to envision all the variables that affect installation and operation on the drawing board, so there should be room built into the plan to make adjustments as needed during installation.
Planning assembly line processes and the flow of materials means interpreting the dry process flow diagram of your intended product into the simplest possible configuration of employees and equipment. Typically, the flow of actual physical materials should correspond with the step-by-step process detailed in the product flow diagram. In addition, the planning stage should account for product flexibility, as products and demand change over time. As you plan each assembly phase, consider the fine details, such as:
- How will materials arrive at this station? Can you shorten the distance or simplify the method of conveyance?
- How much work can be done at this station? Is it possible to affect multiple process stages in a single physical location?
- How will products travel to the next station?
- Does this station need to wait on the finished work of one or more previous stations? Can you create sequences in parallel to minimize bottlenecks?
- How will employees arrive at the station? Will the tools they need be stored here or will they need to transport them?
- What will the workflow for employees be—which hand will do what in which order?
- Is it possible to maintain the same product orientation as the last station and the next station? Can the product be assembled from top-down?
- What safety measures do employees need? What ergonomic solutions should you provide?
- How will you remove waste from this station? Is there a simpler way?
- What are the power requirements for this station? How will you connect equipment to the power source?
- How will this station be maintained? What are the service requirements for this equipment? How will maintenance workers access needed areas?
- How much flexibility does the ideal setup for the intended product have? Can this setup accommodate a range of similar products?
Once you have determined answers to these questions, you can move forward to setting operational and quality assurance standards.
Determining and Implementing Operational and Quality Assurance Standards
Each assembly stage should meet measurable standards. These standards range from production speed to specific torque values for fasteners. Such standards form the actual framework of production—without them, workers are left to guess at values and managers are left to assign quotas based on intuition. Then nobody really knows if they’re doing it right or not.
In addition to developing standards based on designer recommendations, it’s essential to establish a process for ensuring that these standards have been met. Quality assurance processes should cover each aspect of assembly, including:
- Inspection of raw materials
- In-line observation of products as they move from station to station
- Employee training, performance, and satisfaction
- Calibration and testing of tools and equipment
- Inspection of completed products
Not every single product needs to be inspected at every single stage. Rather, you should develop a statistically significant testing regiment that considers the risk assessments your quality assurance professionals identify.
An example would be determining tool calibration intervals. Intervals should not be determined by the tool’s average, advertised, or expected failure rate but rather by the amount of risk an improperly calibrated tool poses the company. Critical applications where failures can be costly, dangerous, or life-threatening demand shorter calibration intervals and more rigorous product inspection. This is not because the probability of failure is higher but because the repercussions are more severe.
Certain aspects of quality assurance, such as employee satisfaction, are more difficult to measure than others. However, they are still critical. After all, satisfied, engaged workers are more likely to meet performance standards and make fewer mistakes.
Designing an assembly line can be an invigorating challenge for the manufacturing engineer. Achieving an optimal solution, which can produce a range of similar products, takes careful planning and considered questioning. By paying attention to details in process flow, establishing standards, and inspecting results, engineers can design assembly lines that are both effective and elegant.
