Design for Handling (DFH): Part Two of our series Design for Manufacturing. See the first post about Design for Assembly here.
Have you ever tried to pick up a coin from a polished floor? Or maybe you have tried to pick up a wet spaghetti noodle? How long did it take you? Chances are, it took you longer than you thought it would. Now imagine you were forced to pay for the amount of time it took you to pick up that coin or noodle. I’m guessing you would be extremely frustrated that you were wasting money on something that shouldn’t take much time. Unfortunately, this is the same type of situation many companies face daily. Workers on assembly lines fumble with small, slippery, or sharp parts in their effort to assemble them into products. Each part takes more time than is needed to retrieve, handle, drop, handle again, etc. This problem is not the fault of the worker. It was created by the engineers and designers.
Besides making a worker’s job more frustrating, the effort spent in excess handling is nothing more than a waste of time, energy, and money. Optimizing part handling is a simple way to save your company lots of easy money and make your workers happier in their jobs. Let’s take a few minutes to look at six common downfalls and specific ways to remedy these situations with Design for Handling (DFH).
Key Points for Design For Handling & Pitfalls to Avoid
1. Small Items
I personally have had to grasp and install 1/16th-inch diameter roll pins. I still shutter at the thought of picking them up, let alone picking them out of a parts bin. If one ever fell on the floor, I just gave up and searched for the broom. Avoid or reduce small, difficult-to-grasp parts wherever possible. If a small part is unavoidable, add features which will make it easier to grasp and manipulate. For example, add a 90-degree bend or a textured surface. When appropriate, invest in ways to organize and present the small parts to your workers. This will save both time and frustration. For example, adding temporary handling tags or automatic dispensers will quickly pay for themselves at scale.
2. Cumbersome Shapes
The perfect example of a cumbersome shape is the coin or flat washer. In one orientation it’s large and easy to grasp. From the other orientation, it’s a flat smooth item. In Design for Handling, part shape needs to be considered when trying to optimize for assembly. Adding or specifying features which make the parts easier to grasp in all orientations will help reduce assembly time. Features such as holes, bolsters, or flat-grip points can help the worker get a better grip. Something as simple as a grove or heavy chamfer around the edge will help someone lift an edge high enough to pick it off even the smoothest floor.
A very common design oversight is how easy parts are to grip regardless of size. Usually slipperiness is only considered when a part is dripping with grease or lubricant. However, some part shapes all but guarantee you need a second or third hand to insure it will make it from the bin to the assembly. Part shape combined with a smooth finish or low-friction material makes life even more interesting. For example, I once had to assembly a small, round, chromed-plated magnet. Under normal circumstances this component would be easy-to-handle. However, due to the round shape and chrome plating, if the magnet ever got wind of iron—it would slip from my hand like it was covered in oil. Each time I’d have to stop, try to regrasp it, and make a second attempt. Stopping time is all time being lost. In the case of the magnet, investing in a simple pair of high-friction gloves was enough to decrease assembly time. Likewise, applying an easy-to-manipulate jacket or a dispenser which ejects the magnets at the point of assembly would all have helped. Other options would be to add texture for facets where possible.
Sometimes parts are the opposite of slippery; they can be inherently sticky making it difficult and time consuming to handle. Parts can be sticky because of adhesives, but more commonly they can stick from vacuum/suction force or from being wet. For example, freshly-cooked pasta seems to weld itself to countertops despite being extremely slippery. The same is true with heavily-oiled washers or shims. The surface tension will cause multiple washers to stick together. Likewise, tight-fitting components will often stick together from nothing more than vacuum force. Cup-shaped objects are notoriously prone to this. Sometimes, adding a feature or a lining to help prevent part suction will easily pay for itself by reducing handling time.
We all have dropped a thumb tack or a pin at some point (no pun intended) in our lives. Have you ever noticed that the orientation of the tack or pin will determine how fast we pick it up? Humans don’t like getting pricked, stabbed, or hurt in general. Asking someone to reach into a parts bin to retrieve something that may bite them will inevitably slow them down. By simply breaking or smoothing the sharp edges off a component, it will help speed up assembly time and increase safety. However, sometimes the sharpness is the design intent of the component. In those cases, design the part to be more like a thumb tack when possible. Design for Handling in this example could be adding handles, flats, or grasp points to give those fingers a safe avenue of approach.
In my opinion, the flexibility of a component is one of the most overlooked labor adders that I’ve come across. Something as simple as a wire harness or a brake cable shouldn’t be that hard to install, right? Yet somehow, they always seem to have a mind of their own and want to face right instead of left. Flexible components have the added challenge of getting matted and tangled inside a box or parts bin. Combine this with a slippery or sticky finish and we have a wet-noodle situation again. When multiple sticky, slippery, flexible parts are paired together, the company is paying as much for the worker to unknit them as they are to assembly a product.
By implementing these small pieces of design for handling, you can prevent workers from needing a second or third attempt to assemble a product. After all, we are only human. Some parts are just too impractical to handle efficiently due to their size, slipperiness, stickiness, sharpness, or flexibility. Stubby-fingered humans need extra time to grasp and manipulate these items. Even the most sophisticated robots have trouble without even more sophisticated tooling. A golden rule is to always try to reduce the number of parts and keep the assembler in mind when designing products. By planning for assembly, components can be designed for quick, easy assembly. This will save significant time and will boost your productivity, lower cost, and improve the worker’s experience. The faster a worker can grasp, retrieve, and handle a component is all potential money in the bank.
If you think there are opportunities to cut costs through Design for Handling in your manufacturing operations but not sure the specifics, give us a call or contact us today! Our mission has been helping manufacturers save money and cut unnecessary costs for nearly 20 years.