White Paper: Optimizing Frame Design & Production

Eric Hill, Plataine

 

The need for Optimization

Customer demand for greater variety and shorter delivery times coupled with intense global competition are pushing upholstery manufacturing to seek new ways to optimize production. The shift from traditional stick-built frames to plywood engineered frames and CNC cutters has been one of the most fundamental changes the industry has made to address these new economic realities. With new materials and technologies in place, new methods are required, including a fresh, efficiency-minded approach to frame design and production.

 

Design with structural strength in mind
The #1 rule every frame designer must to keep in mind is making all parts support each other. The basic idea is simple; you can look at it as the tent pole effect. A tent pole is weak without the guy wires in place to support each other. The same goes for an engineered frame; its strength comes from all the pieces being locked together to support each other.
All joints should be attached to each other using either staples, nails, screws, or any other fastening device in a bidirectional pattern. However, a strong frame design should never let a piece just but up to the connecting piece and depending on fasteners to hold it in place. To ensure the structural strength of your frame, every piece should either intersect or interlock with its connecting pieces.

Using a 3D design software package allows you to design these parts to create a more structurally sound frame. It can also help you reduce the cost of material and enhance the look of the piece. Using foam and other filler material in an upholstered piece carries a significant cost. Use the software’s advanced design capabilities to shape the piece instead of filling it out with filler material. This will not only reduce the cost but will also guarantee consistency in how the piece looks no matter which upholsterer built it.

 

Utilize the full potential of your CNC

Frame designs come in many forms, from a detailed drawing by a designer to a napkin sketched over lunch. Upholstery manufacturers transitioning from traditional stick-built frames to engineered frames are converting their existing designs to electronic formats that can be translated into the code fed into their CNC machines. However, by doing so, they fail to take advantage of the opportunities offered by the CNC machine.
Traditional frame designs were constricted by the limitations of the material and the tools used for frame construction. With CNC machines, the old saying “you can draw anything but you can’t make what you draw” no longer holds; a CNC machine can cut almost any shape imaginable.

Rather than mimicking the old frame design, 3D design software enables you to construct a frame that takes advantage of new possibilities offered by CNC machines. It allows you to design interlocking parts and visualize structural problems before the frame is cut and assembled, things that were just not possible or practical using hand-drawn design methods and traditional cutting tools.

 

Simplify designs for your CNC

With 3D design software on your desktop and a CNC cutter on the shop floor, you can make these frame parts almost any shape and size you can imagine. But that doesn’t necessarily mean you should. CNC machine time is a valuable resource that should be carefully utilized. Even though a CNC cutter is much faster and less labor intensive than the old ways of cutting wood, making compound cuts can easily double or triple machine cycle time. A good designer will take this into consideration and keep the frame design as simple as possible.

For example, in first glance a part may look like it could only be cut using an angled or miter cut. By carefully examining the surrounding pieces, you may find a way to change the design of the part and end up with a more simplistic frame utilizing through cuts that take less machine time.

 

Choose the right material for your product

What material should I use? This question is commonly brought up in every upholstery manufacturing environment. Attempting to keep the cost of material down may lead a company to engage in frequent material changes. While many parts in a frame can be made from a less structurally sound material, others cannot. For instance, a rail supporting the weight of a person should always be made of solid wood plywood rather than OSB or some other particle board.
In many cases, it is more cost effective and logistically simpler to use a single, more expensive material and avoid mixing materials altogether. Using a number of different materials will force the CNC operator to stop the machine and slowdown the process. The loss of machine productivity and the increase in labor involved with this extensive material handling may add up to increase your total cost of production beyond the anticipated savings.

 

Make design work for your assembly

Keep in mind that your frame design dictates the flow of the piece through the plant floor. Designing a frame with many small pieces may produce greater material yield, helping keep cost down. At the same time, using fewer parts will increase productivity and reduce labor requirements throughout the plant. This is a tradeoff that you have to be mindful of and balance based on your own company’s cost parameters and goals.

 

Avoid over-cutting

The scenario is familiar to every person that has spent any time in furniture production. It starts with an order for one sofa. More than likely, that sofa will require over one sheet of plywood but not quite two, leaving you with a portion of a sheet of scrap. To avoid plywood waste, the common solution is to nest two sofas over three sheets so there is no scrap left.
The problem starts once we have the extra cut frame waiting for a new order to come in. First, the frame parts have to be stocked in inventory, with the hope that none of the parts get lost in the meantime. Assuming we got lucky, a month later an order comes in for the same sofa; but this time it is for three sofas, so we are going to use up our inventoried parts and cut two additional new frames.
However, in the fast-paced world in which we operate, there is a good chance that in the month that elapsed between the two orders there was a design change, and all of a sudden the frame that was on the shelf is no longer up-to-date. Not knowing there is anything wrong with it, the frame is pulled from the shelf and sent to production. Only when the frame-builder starts assembling the frame, off goes the alarm and over come the supervisors and find out this is an old design. So the old frame gets trashed and a new frame has to be cut, and our story starts all over again…
Not only was plywood wasted, but significant labor cost was incurred in the process of first cutting the extra frame, then moving it to a storage shelf, taking it off the shelf and sending it to production, and finally discarding it.
This common scenario shows how a practice that was intended to avoid waste ended up throwing a monkey wrench into your production process, as the entire upholstery line flow was disrupted. This is just a simple scenario with a small quantity of frames; just imagine what happens in a large factory producing hundreds of frames each day.

How do we avoid over-cutting? What we want to do is cut that one-sofa order and instead of cutting another identical frame for inventory, use whatever is left of the second sheet to start the next order (for a different frame). The method is called Rolling Nest - it is like putting the plywood on a roll but keeping all parts for different frames separate.

By only cutting what we need, we not only save on material and labor cost, but we also free up space that was occupied by inventory bins with frames that collect dust.

 

Streamline the coding of your CNC machine

Once the nesting of the frames is done, a toolpath has to be created and the G-code has to be entered into the CNC machine in order to execute the cut. Done manually, each step in the process can be both time-consuming and a source for damaging errors.
Using a program that automates toolpath generation and the creation of G-code for your CNC machine can save valuable production time and eliminate potential failure points. It also frees up your programmers and designers to produce new fresh designs rather than spend their time on tedious tasks.

To make things even easier for your CNC operators, the program can generate printouts for each nest, letting the operator know in advance exactly what the machine is going to cut. With the addition of a barcode reader, all the operator has to do is scan the barcode, press the cycle start button, and let the machine do the rest.

 

Choose CNC machines that best fit your product

CNC choices are abound, with options ranging from vacuum, roller, vacuum and roller to twin tables, single table, tool changer, drill banks, and the list can go on and on. The most important factor in making your selection is matching the machine features to your product characteristics.
For example, if your product requires special operations such as roundovers or degree cutters, you might need a CNC with an automatic tool changer; or if your product requires a lot of drilling, you might choose a drill bank that can hold multiple bits.
Consider the material you plan on using. If the material you are going to cut is a Grade A material, a vacuum might be all that you need; but if it is of a lower grade with some warping, you would probably need both a roller and vacuum.
Since the purchase of a CNC machine is a long-term investment decision, it is important that you consider these factors not just for today, but also for the future as you adjust your product design to streamline production.

 

Control the feed and speed of your CNC machines

Every so often, you will hear a machine that could almost pierce your ears with a squalling sound. It will usually happen when the spindle Rpm is wide open and the machine is cutting at full speed. Yes, we all want the most productivity from the machine, but this doesn’t always equate to maximum spindle Rpm.
Operating a cutter is part science part art. You can get started by using a chip load calculator, then tune it by ear from there. The calculation is rather simple:
Chip load [in.] = feed rate [inch per min.] / (RPM / # of flutes)
Experience shows that a good chip load is somewhere in the range of .02 to .06 inch, as this load helps dissipate the heat from the tool and lengthens the tool life. If you start, for example, with a feed rate of 1200 inch per minute and 22,000 Rpm, you will end up with a chip load of .02 inch using a 2-flute bit.
From here on, you have to use your ears to fine-tune the sound of the bit cutting by adjusting the spindle speed up or down. You know you are there when it sounds like tearing a piece of paper. That’s the art part.

 

Select the right tools

Speaking of tools, there seems to be an overflowing selection of tooling to choose from these days, and a new tooling manufacturer around every corner. When choosing a tool, make sure the vendor can guarantee the quality of the tool.
Use the right tool for the speed and finish you plan to achieve, keeping in mind the material and the machine characteristics. For example, if your machine will only cut 600 inch per minute and only turn 18000 Rpm, you don’t want to use a 3-flute tool which will make the chip load too low (<0.02) and cause it to start burning. In this case, you may need a 2-flute tool instead.
Remember that every tool is going to be different. When you reorder the next batch, while the new tools may look visually identical, they may function slightly differently. You may need to make feed and speed adjustments to accommodate such differences.

 

Summary

While many of the challenges faced by upholstery manufacturers are the result of global trends outside our control, there are things that every manufacturer can do to combat these challenges. Staying competitive in this day and age requires all stakeholders - managers, designers, programmers and operators included – to scrutinize every step and find new ways to better serve the customer, increase process efficiency, and make the most out of new technology innovations. Frame design and production are important parts of the process; we hope this paper provided you with some ideas you can implement in your factory.

Please fill out the form below to download your copy.