Structured Approach to Material Supply for Assembly – Part 2

It is sometimes a challenge to provide material for assembly. In this second post I will continue with the different aspects and steps to consider when creating an assembly location. Enjoy!

Fit Your Parts around the Station

Now you can start to fit your parts around the workstation. Ideally, all parts are within easy reach of the operator.

Car Seat Assembly
Your unfinished product is usually the biggest part.

Most important is usually the unfinished product, since it is often the largest item that has to pass through the workstation. The worker will receive the unfinished product, work on it, and then move it to the next station or to storage. In an assembly line, this is for small products often a move from one side to the workspace to the other side, or for larger products something similar to an automotive assembly line.

All other parts go into these unfinished products (with few exceptions, as for example packaging material). There are two approaches that are commonly used to arrange these parts, and both are sensible. Usually it is best to do a combination of both, which requires some back and forth until you have a suitable solution.

Start With the Bulky Parts First: One approach is to start with the biggest and heaviest parts. They need most of the space, and are also difficult to handle. Starting your material supply structure with these will give them the best spots, which makes it easier for the worker to assemble. If you need gear to lift heavy parts, it is easiest to fit in if nothing else is in the way (yet).

Start With the Most Frequently Used Parts First: The other approach starts with the most commonly used parts. Putting these “A” parts closest to the worker will make them easier to reach and will reduce overall work time.

Both the “bulky parts first” and the “most frequently used parts first” strategies are valid. Best is probably a combination of both. Get the really big parts out of the way, and then continue with the “A” parts.

Location of Parts and Ergonomics

Ergonomics likes to split the workspace into different zones. The easiest to reach first zone is around elbow height and in front of the worker, accessible by moving only your lower arms. This should be where most of the assembly work happens.

A second zone is accessible by moving the entire arm, giving the worker more reach. This can also be a bit higher or lower than elbow height. Everything is literally an arm’s length away. This is the best spot for your material.

A third zone can be reached by not only stretching your arm but also bending your body. This could also be behind you, reachable by twisting your body.

The fourth zone is everything else. The worker now has to walk to access this zone. A simplified view is given below. Note that for the work table on the right, I kept some space for the part to move across the table.

It should be pretty clear that the closer you can get the parts to your worker, the easier and faster the assembly is. Ideally, parts are supplied in front of the worker above or next to his assembly space. Of course, this is not always possible. It is difficult to supply big parts across the assembly space.

How to Provide Parts

No matter where you put the parts, they have to be somewhere. This could be as basic as a pallet on the floor, although this is, ergonomically speaking, not very good. An improvement may be a pallet on an small lift as shown in the adjacent image. Using such a device can reduce the stress for the worker by providing parts always at a suitable height.

Warehouse rolling rackIt could be simply a shelf with parts on it. However, here too it may be better to use rolling lanes that can be filled at one end and emptied at the other. This simplifies the filling and maintains FIFO. A full box is always behind the next box. This is common for supermarkets for small- and medium-sized parts.

There are also options for chutes and slides to provide parts as shown in the adjacent image.

Chutes are often simply plastic tubes that are filled at one end and emptied at the other one. If you use a clear tube, it is easy to see how much material is in the tube. This is a form of visual management. Often, foam rubber at the end of the chute makes picking up small parts easier. This is similar to some coin trays in Japan with a rubbery bottom.

The exact way of delivering the material depends on your specific situation, but feel free to be creative. You should always make sure that the material is easy to add and easy to remove, and that the quantity available is easily visible. As mentioned earlier, you may also provide lifting devices for heavy parts or other tools for parts that require special gear.

Delivery of Information

You should not forget that the worker needs not only parts but also information. There are generally two bits of information needed: what to produce, and how.

What to Produce: The worker needs the information on what product to produce. In an assembly line, this may simply be defined by the part that is handed down from the previous station, and often only the first station would need information on the product type. This information may also be needed along the line if the worker creates different variants from the same unfinished product.

If the products come in batches, it may be easier (“in the morning we do A, in the afternoon B“), but lot size one is usually better in lean. If your only reason for a batch size is the information flow, then don’t, and do lot size one instead. Find a way to inform the worker what the current product is going to be. This could be, for example, a sheet of paper attached to the product or a digital display.

How to Produce: The worker also needs to know how to produce the product. This could be a simple work standard printout or a more fancy pick-by-light, where a light indicates which part to use next. This topic also deserves its own blog post, and due to the scope of this article, I won’t go into details here.

Access and Escape Routes

Finally, you should also make sure your worker can get in and out of the workspace, and  has the necessary escape routes. The place should be well ventilated, lit, and overall a safe and comfortable workplace. Usually not a big issue, but you should not forget.

So, this is an overview of the most important aspects to consider when creating an assembly workplace. It is no magic, but simply focused work and common sense. In my next post I will go into details about how to deal with space limitations. What can you do if you are running out of space at your assembly location? Until then, stay tuned! Now, go out and organize your industry!

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