3D knitting, is it worth it?
Many people confuse 3D knitting with 3D printing. Knitting is additive manufacturing, but there are so many more variables. Each variable needs to be adjusted for each plane of knitted structure.
Unlike 3D printing, each plane’s structure and dynamic stability may be different than the adjacent plane. The planes all need to work together as a unit. It is not as simple and easy as the machines may make it look. There is a lot of unseen planning that goes into each part. to make them accurate. In a medical product, this could mean the difference between a surgery being successful or not. So the real question is, do you need a high rate of accuracy in each piece? If yes, 3D knitting is probably for you. 'Great', you might say, 'make me a prototype.'
The old saying, ‘if it was easy, everyone would be doing it,’ is very true in this technology.
There are many considerations that need to be weighed in pursuing 3D knitting projects, not just the cost of the actual knitting. If one know their way around a cost sheet, cost is a combination of fixed overhead and variable costs, such as labor, materials, and finishing processes that go into making a product.
In knitting to shape some labor actions and materials are eliminated or shifted into other columns. For instance, if a product or a component is knit to shape, there is no cutting or fabric cost, but there is raw material cost in yarn because fabric is being made at the same time as the product or component. It is also true that not everything needs to be made 3D all in one piece. Some things need to be knitted to shape, 2D. Knitting to shape creates integrity in the edges, nothing unravels. The same yarns travel throughout the piece.
neck band knitted turned cloth - (Thanks Maria, our model)
Stitches are dynamic, shift, and move. Things in kntting just don’t happen as fast as rendering a Solid Works file for a 3D printer and leaving it overnight to materialize. Stitches are alive in a product, and take precise engineering, especially in the dynamics of multiple planes. One can not just program and let the machine do its thing. A good engineer does not leave the machine to just run, but watches each part of the piece as it is knitting to understand why something might be straining. The technician then can make adjustments, as he or she sees is needed. Some of them may seem minor enough, but small tweaks increase speed and reduce damages. In thousands of pieces this is exponential savings in time, and damage factors.
3D integrated medical product from 1989
The other truth is that, today, 3D has become such a buzz word that it can be used interchangeable, depending on who you are talking to. Here are some clarifications:
Fully fashioned is 2 D knitting to shape. This produces finished edges that will not unravel. In the past, most women’s wear didn’t show fashioning marks and men’s wear did. To show fashion parks a flat machine replicates the fashioning points on a Scheller, Steiger or Bently full-fashion frame machine, moving 3 to 5 needles on the edge into the fabric at a time, so it appears a block of stitches moves together. The pieces are linked or cup seamed together.
Whole Garment or Knit and Wear are apparel approaches to flat knitting where the whole product is produced by the machine with no cutting or sewing. These are technically seamless, but fashioning marks or lines may be seen in the fabric where the yarn stretches the gap of the needle beds.
Seamless Knitting is usually associated with Lonati / Santoni circular machinery. The fabric is knit in a tube format, like making a sock. Stitch tensions can be increased or decreased, but needles can’t be added or subtracted. The edges, which are cut to make sleeve hole openings, and shoulders must be finished. The diameters of the machines are typically body sized and it’s the side seams that are eliminated for a nice feel on the body. The tops and bottoms of the tubes need to be finished, but the speed is exponentially faster than flat knitting.
3D Knit means knitting to shape, but knitting multiple planes or facets. In medical products and footwear amongst other products, this adapting the shape to what is needed creates anatomically correct products or components: elbows, knees, heels, etc. Think of the difference between a 2D picture and a 3D sculpture. Most times the 3D product can stand on its own without help and can’t be packed totally flat. Above is a 3D integrated medical foot application. We say it is integrated because we are creating several zones, integrating different stitch structures and multiple types of yarn, all in one piece.
4D Knit means knitting 3D but also knitting in components like wiring, conductive materials, composites, or leaving voids to allow insertion of hardware, sensors, stays, hinges, or other secondary components.
5D Knit, if you’re keeping up, means knitting can be all of the above, but also knitting in components that change under different circumstances. They can be one way or reversible, meaning that the fabric needs to shift with the change and then go back to the original state repeatedly.
One may say, this multi-dimensional knitting is great technology, but what does it mean to me if I’m not NASA or a medical company that needs fifteen years’ worth of product life cycle?
whole garment dress with nearly zero waste.
Knitting to shape has many benefits, one of which is the reduction of waste. Having finished edges, no cutting, and easier sewing is a great benefit of 2D knitting. Some care must be taken to make sure the pieces match, and that the resulting garment, or product fits, especially if the pieces need to be assembled prior to dying or washing. Different colors may react in dissimilar ways, and depending upon fiber type, or if the yarn was packaged dyed or solution dyed.
Eliminating human error
Knitting in 2 and 3 D features puts each component in the exact same spot every time, finished or partially finished, ready for next steps, buttons, labels, etc. The machines do not get tired. And, if they are well maintained, they rarely break down.
In the cutting room, fabric must be laid out, layered, and left to relax usually over night before cutting. Some lays can be up to 200 plies. If the fabric is cut by hand, the cut is only as good as the cutter and his/ her tools. There is risk of the top layers shifting and skewing, layers fusing together if the blades are to fast, the cutter's arm is not long enough. If it is automatically cut, most of those issues go away. Regardless, the first thing that needs to happen to fabric after it is cut is to stop it from unraveling, securing the raw edges. Typically this is done in overlocking, where a bit of the fabric is also trimmed away. If a pocket is needed, typically holes are drilled in the stack of layers for where the pocket is to be located. If a hole is drilled, that hole needs to be secured in the pocket process to stop unraveling.
Then ask how much time and money is the average cut and sew flat knitted garment putting in the trash? How much is spent on labor, space and tools to cut the pieces, accumulate, remove and dispose of the trash? How much is spent to overlock the cut edges not to unravel, and QC?
Any production engineer will tell you that aside from the thread type and seam construction, it mostly depends on who is sewing, their work load, and when. Is it a new person or the sample maker? Many things can affect sewing quality from the time of day, fatigue from the sewing process itself. Many of the actions like button holes, making plackets, creating pockets, and getting them straight and accurate could be done by the knitting machinery. Specialty sewing applications still exist. But the people that were in the cutting area and sewing could be moved to much safer jobs in the knitting room.
The WYSIWYG software for knit design offered by most knitting machine builders is visual, and are relatively user friendly. Seeing what is happening on the computer screen allows for rapid prototyping, including knitting to shape.
The challenges of knitting all in one piece are many
For apparel, we have steered away from knitting the complete product completely-finished from the machines, except where the client insisted. Sometimes the buzz word 3D is what they heard, but something else is what they really need for their product, price point, and market position. The main issue of 3D is the limitation of stitch types. The second and toughest issue is that some of these garments take 3 hours for simpler designs, and several more hours for complex garments. Three hours can mean $45.00 worth of knitting on that cost sheet, at 100% perfect production.
T- shaped dress with pointell, jersey, and links links. 180 minutes from Stoll library on a 7.2 knit and wear
The main limitation to knitting garments or products all in one piece, is that all the fabrics used in the piece need to be jersey based or half-gauged versions of double bed fabrics. To transfer any loop, a free needle needs to receive it - somewhere. This can make for a lot of shifting and juggling stitches to get them oriented – in other words, a lot of time with no knitting going on.
Talking about time, some of these fashion garments may take three or more hours for a simple product, mostly because of all the transferring needed. Fashion or technical fabrications with excessive transferring, typically need the extra needle beds, and advanced machinery technology – the X machine from Shima and the T machine from Stoll,. Transferring double bed structures always needs these machines with 4 needle beds, both of which take seasoned professionals to program and run optimally. Steiger also has a machine that holds the stitches under the bed and transfers these type of fabrics, but we have not yet seen it in production.
Double bed fashioning from Stoll MT machine
Regardless of machine type, what happens when the piece gets a damage two hours into a piece while knitting? Most times the garment is trash or the piece needs to be unraveled, if the fashioning areas can be navigated, and reknit into something else. This takes a lot of time to unravel, and most companies, unless they are using cashmere or a high-end yarn, will just scrap the piece rather than putting more money into it. If you notice any of the the knit all in one piece garments from any machine manufacturer, all of them have good yarn, not cheap yarn. You will not see open end carded cotton in a 3D garment. The machines really work the yarn, doing all the transferring to make this 3D all in one piece possible.
Yarn for this sample is from Lineapiu
Even with great yarn and WYSIWYG, it still takes thought and the time to plan, engineer and program garments all in one piece.
Some things work well in Jersey based fabrics. Other products do not. The main focus in developing any product is making it practical and cost effective. Most higher end garments need either expensive yarns or double bed type fabrics. The perceived value of a half gauge or a jersey garment may not meet consumer expectations in all markets. Jersey fabrics and half gauge double bed may be fine for some apparel, but not for technical textiles that need to perform a function and need to hit specific tolerances.
1. No cutting
2. No sewing minimal waste
3. Ready to finish, pack and ship
4. Newly zero waste
1. Limited to jersey based fabrics – no double bed jacquard
2. Most cases limited to ½ gauge (looser knitting)
3. Collars look limp
4. Consumer perceived quality does not justify high price
5. Extraordinarily long programming can be 100 hours+ for one style
6. Long knitting times – 1 to several hours per garment
7. Damage at the end ruins the whole garment
8. Clients like to use inexpensive yarns – does not work well in cotton
Sometimes, 3 dimensional knitting a perfect fit. And other times, the true solution is going back in time and looking at old school solutions in a new way, with today’s more powerful CAD system and modern faster knitting machines. For instance, eliminating seams that that take a minute or two to sew in 2D, but 20 minutes, an hour or more, extra to knit in 3D, is not practical, nor does it warrant the price increase. For a simple garment, a hybrid may be preferred – multiple components with simple cup seam assembly that knit in 1/3 the time or less. Sewing sleeves on significantly less expensive than knitting them on and finished with transfer marks they might not like.
It 3D knitting to shape worth it? It truly depends on the market, the volume, and price point – what the end consumer is willing to pay. Follow the money. If problem can be solved with a low-tech solution and the customer is not going to pay for the over engineered, but cool solution for the same result, do the low tech. There are a number of factors that affects the yes or no of if the end consumer will purchase and not return a product - performance, reliability, durability, visual and perceived quality of the product.
As in any business decision, give the customer what they want. If the end customer appreciates the technology, and is willing to pay for it, there’s a practical business reason to use it.
So, in choosing cut & sew, 2D, 3D or beyond, choose your path wisely.
Connie Huffa – Fabdesigns, Inc.
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Newsletter for manufacturing technical textiles & 3D flat knitting
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3D knit pointelle top Concetta Bruce original design