Routing and Work Centres: Building Your First Realistic Routing

At its core, a routing is a detailed specification of the path a product takes through the factory. It defines the sequence of operations required to transform raw materials into a finished product, including the work centres where each operation occurs, the operation times, and the tools or machinery used. Think of it as a recipe for your product: just as a recipe lists ingredients and steps, a routing lists the manufacturing steps and the resources needed.

Routings are fundamental to several key business functions:

• Production Planning: Routings determine how long it will take to manufacture a product, which is essential for scheduling production runs and meeting customer deadlines.
• Capacity Planning: By knowing which work centres are used and for how long, you can identify potential bottlenecks and balance workloads.
• Costing: Operation times directly impact labor and overhead costs, so accurate routings are crucial for pricing and profitability analysis.
• Quality Control: A well-defined routing ensures consistency in production, reducing variability and defects.

Without a realistic routing, your production planning is based on guesswork, which can lead to missed deadlines, overworked machinery, and unhappy customers.

A work centre is a specific location in the factory where a particular type of work is performed. It could be a single machine, a group of identical machines, or a team of workers. Work centres are the building blocks of your routing; each operation in the sequence is assigned to a work centre that has the appropriate capabilities.

When defining work centres, consider the following:

• Capabilities: What operations can this work centre perform? For example, a CNC machine might be capable of milling, drilling, and tapping.
• Capacity: How many units can it process in a given time? This is often expressed in hours per day or units per hour.
• Efficiency: Does the work centre operate at standard efficiency, or is it slower due to age or maintenance issues?
• Setup Time: How long does it take to prepare the work centre for a new job? This can significantly affect operation time.

In your routing, each operation should specify the work centre to be used. This allows planners to see at a glance which resources are required and when they are needed. For example, if you are manufacturing a metal bracket, your routing might include operations such as cutting (work centre: band saw), drilling (work centre: drill press), and finishing (work centre: grinder). By clearly defining work centres, you can ensure that each operation is performed by the most suitable resource.

Operation time is the time required to complete one unit of product at a specific work centre. It is a critical metric because it directly impacts your production schedule and costs. However, many manufacturers struggle to estimate operation times accurately, often relying on rough estimates that lead to inefficiencies.

To build a realistic routing, you need to consider two components of operation time: setup time and run time. Setup time is the time to prepare the work centre for the job, such as changing tools, loading materials, and calibrating machines. Run time is the actual time to process one unit once setup is complete. Both must be accounted for in your routing.

Here are some tips for estimating operation times:

• Use historical data: If you have been manufacturing for a while, look at actual production times from past orders. This is often the most reliable source.
• Conduct time studies: Observe workers performing the operation and measure the time with a stopwatch. Do this several times to get an average.
• Consult machine specifications: Manufacturers often provide cycle times for their equipment. Use these as a baseline, but adjust for your specific conditions.
• Factor in allowances: Include time for breaks, machine clean-up, and unexpected delays. A common allowance is 15-20% above the raw time.

For example, suppose you have a drilling operation. The machine specification says the cycle time is 2 minutes per part. However, you know from experience that loading and unloading takes another 0.5 minutes, and there are occasional machine jams. Your operation time might be 2.5 minutes plus a 10% allowance, totaling 2.75 minutes. By being realistic, you avoid overpromising on delivery dates.

Now that you understand the core concepts, let's walk through the process of creating a realistic routing for a simple product. For this example, we'll use a wooden toy car.

Step 1: List the Operations

Break down the manufacturing process into individual operations. For the toy car, this might be:

1. Cut wood to shape
2. Sand edges
3. Drill axle holes
4. Assemble wheels
5. Paint
6. Package

Step 2: Assign Work Centres

For each operation, determine which work centre will perform it. In a small shop, you might have a saw, a sander, a drill press, an assembly bench, a paint booth, and a packaging station. Assign each operation to the appropriate work centre.

Step 3: Determine Operation Times

Using the methods discussed earlier, estimate the setup time and run time for each operation. For example, cutting wood might take 1 minute per car, with a setup time of 10 minutes to change the blade.

Step 4: Sequence the Operations

Arrange the operations in the correct order. Some operations may be parallel, but for simplicity, we'll keep it linear.

Step 5: Document the Routing

Create a routing sheet that includes the product number, operation numbers, work centre codes, operation times, and any special instructions. This will be used by production planners and shop floor workers.

Here's an example of what part of the routing sheet might look like:

By following these steps, you can create a routing that is both realistic and useful for planning.

Even experienced manufacturers can fall into traps when creating routings. Here are some common mistakes and how to avoid them:

• Overly Optimistic Operation Times: Underestimating how long an operation takes is a frequent error. Always add a buffer for variability.
• Ignoring Work Centre Capacity: Just because a work centre is assigned doesn't mean it's available. Check that the work centre has enough capacity to handle the scheduled volume.
• Not Updating Routings: As processes improve or machinery changes, your routings should be updated to reflect new realities. A routing that is three years old may be obsolete.
• Failing to Include Quality Checks: Quality inspections are operations too. Including them in the routing ensures they are not forgotten.

By being aware of these pitfalls, you can refine your routing to be more accurate and effective.

Building a realistic routing is a foundational step towards efficient manufacturing. By understanding the role of work centres, accurately estimating operation times, and avoiding common mistakes, you can create routings that streamline your production planning, improve capacity utilization, and enhance profitability.

Start by reviewing your current processes and identifying areas where routings are missing or outdated. Use the steps outlined in this guide to develop routings that reflect the true capabilities of your factory. Remember, a routing is not a static document—it should evolve with your business.

Ready to take your production planning to the next level? Begin by mapping out your work centres and operation times today. Your future self (and your customers) will thank you.