Pick by Stencil – AllAboutLean.com

Pick by Light is a well-known technology in manufacturing to simplify the picking of multiple parts for kitting. It is a proven technology, albeit setting it up is still time-consuming. In this post I would like to show you a low-tech alternative that I have seen at the BMW Group Dingolfing plant: Pick by Stencil! You use a pattern, stencil, or jig to have one slot for each part of this particular pick. Another pick simply uses another stencil. Let me show you…

The Challenge

Picking is an important subsection of kitting (i.e., generating kits to be used for a certain product). In picking, you have to pick a number of different parts to match the corresponding bill of materials (BOM) or a subsection thereof for one product. It is important to make sure you have nothing forgotten and that the parts are of the right type. Especially in modern industry, many parts look very similar but are in fact different. Just relying on the memory and attention of the picker is asking for a lot, especially if the person is picking for longer periods of time. A missing part will slow down or stop production. A wrongly picked part can damage the product, lead to defects, and even cause harm to the customer.

Pick by Light

Pick by Light (sometimes also called Pick to Light) is a warehouse order fulfillment system that uses illuminated display modules at storage locations to guide pickers. When an order is processed, the relevant display lights up, indicating the exact quantity of items to be picked from that location. After the picker retrieves the items, they confirm the pick by pressing a button on the module. Some systems also automatically track which box has been picked through sensor above the box, possibly combined with a sender worn on the wrist of the picker as in the picture here.

This paperless, visual system significantly enhances picking accuracy and speed, reduces training time, and improves overall warehouse productivity by eliminating the need for traditional pick lists and enabling hands-free operation.

On the downside, pick by light is a larger initial investment into the sensors and the software. The maintenance and updating of the system also usually requires programmers, and hence cannot be done by the shop floor people themselves, making the system overall less flexible to change. Change is especially cumbersome if you need more boxes or storage capacity, which also requires a hardware change.

Pick by Stencil

The alternative is to use a stencil (i.e. a pattern). Below is an example of such a stencil. The picking involves four hex bolts, a pipe, two pipe bends, and a retaining ring (and yes, I totally did not just throw a few parts together for illustration purposes…). The stencil is simply a plastic plate, with holes cut for each individual part, where the shape of the hole matches the part (more about coloring the areas in a bit).

Emptying the Stencil

The employee simply puts one matching part into each hole. When all holes are filled, then the pick is complete, and the parts are transferred into a box. This could be done one by one… but that would mean touching every part twice and having twice the effort. A much easier approach is a simple gadget where you have a sliding separator. This separator is shown below in red. While picking, the separator is in, and prevents the parts from falling down. Once all parts are picked, the slider is pulled out, and all parts fall into a prepared box below. Hence, with one movement all parts are dropped into a box. This box containing one kit is then moved to manufacturing.

Visual Management Using Color

If you have only one type of kit with only a few parts, this would suffice. But in this case the question would be why to do picking in the first place. For picking multiple different part types, you would need multiple types of stencils. And now you can use colors to make the selection process easier! You could give each part number their own color, but then you would quickly run out of colors, or you force your employees to distinguish between jade green, jungle green, and hunter green. Face it, you have to reuse colors.

However, try to keep colors distinct for similar part types. In the example below, the color for hex bolts, internal hex bolts, and round head bolts is different. The color for hex nuts, hex nuts with integrated washers, and cap nuts are different. The long pipe and the long spring are also colored differently. Overall, try to reduce the likelihood of an employee confusing similar part types. It also helps to label the different fields, as well as the entire stencil.

Obviously, not only the stencil gets colored, but also the corresponding shelf. Label AND color the boxes in the same color system as used for the stencil. Different from the image below, it is enough to mark the front of the row of boxes in color, rather than coloring the entire box if you want to use a kanban type of replenishment system.

Technical Details

The stencil could be made out of any kind of plate, but for practical purposes it should be cheap, lightweight, and unlikely to cause injuries. The sharp edges of sheet metal would be a problem, and the thin material would also not hold the parts very well. A plastic plate a few millimeters thick is better. The thickness should allow it to hold the parts easily without them slipping out of their indents. The size depends on the parts that have to fit into the plate. Even larger plastic plates can be handled with ease.

The slope of the slide underneath of the stencil should be designed so that no part gets stuck on the slide. If you have magnetic parts, use aluminum for the slide. Also, again different from my illustration, also close the front part of the slide so nothing falls out at the front.

Proper guide rails both for the stencil and the box ensures both are placed in the correct position, and no part falls outside of the box.

But I Still Want Digital…

You can definitely integrate this pick by stencil in your digital ecosystem. For example, you could require the scanning of the order and the scanning of the stencil to make sure you have the right stencil. You can even have a stencil and a full pick by light system at the same time, where both the light and the color indicates the item to be picked. The advantage of this combined system is an easy picking through the pick by light, and the added security of the stencil of not forgetting a part, especially if you have multiple parts of the same type for one pick. The larger the number of identical parts, the more likely the picker gets the wrong number.

Overall, pick by stencil can be a low-cost and low-tech alternative to pick different similar parts for your kitting. Now, go out, make sure your pickers get it right (be picky about this!), and organize your industry!

PS: Many thanks to Thorsten Ahrens for showing me his excellent shop floor at BMW group Dingolfing! BMW is one of the very few car makers that comes close to Toyota in terms of lean manufacturing (the other one is Nissan).