Headboard Utilizes Twin Sheet Forming
This Headboard is used on a bariatric bed system and constructed using Twin Sheet Forming. It’s function, in addition to being a headboard, is to provide a handle to move the bed. What is unique about the part is that it is twin sheet molded with an aluminum weldment “insert-molded” into the part during the molding process. With the “insert molding” process we can provide additional structure to parts with rigourous requirements. (We show part of the weldment extending from the part in view 2).
Insert Molding Can Result in Challenges
The challenge the “insert-molding” creates in the twin sheet process is the delay between the sheets leaving the oven and forming to the mold. In addition, the time it takes to load the inserts can also create a challenge. The result is that the sheet continues to lose heat and the integrity of the weld can be jeopardized. Additionally, we need to trim the weld “flush”, as shown in view 1, which can potentially exacerbate this potential issue. The removal of some surface area creates the additional problem of removing some of the material needed for a strong weld. Various process controls and molding techniques allow us to overcome these challenges.
Experience and Technique Help Overcome Challenges
One such technique we employ is the use of core pulls in molds. This mold has an articulating feature (core-pull) that positions the weldment correctly during the process, and then retracts to allow de-molding.
View 3 is a label recess, which we mold using the pressure-form technique. The recess had tight radii defining it and making for a pleasing cosmetic pocket for the label.
Once we have trimmed this part, we then foam fill it for additional structure and stiffness. At that point, we attach a colored polycarbonate overlay in another pressure-formed recess.
Twin Sheet Formed Siderail
This Siderail also employs the twin sheet forming process, and is used on the same bariatric bed system. Its primary function is to create a wall to keep the patient in the bed. Additionally, however, the siderail must rotate out of the way so a patient can be removed from the bed. There are four siderails per bed system. This part, as with the headboard, also employs “insert molding”. Thus, we insert a plated steel weldment for additional structure, as these parts must be more robust. We encountered the same challenges as with the Headboard. Here we also “flush-trimmed” the parting line. The purpose of this trim is to make a cosmetically pleasing rail, as shown in View 1.
The mold also has an articulating feature (core-pull) that positions the weldment correctly during the process, and then retracts to allow de-molding. The challenge here is the accurate location of the hinge holes in relation to the molded part (View 3). The mold also has the heated pinch-line to slow down loss of heat at the weld points that occurs during the “insert” process.
Additional Features
We pressure form the part using the twin-sheet process resulting in sharp, crisp radii to provide a cosmetically pleasing recess for the green overlay. In addition, we form a channel into the part to house a ball. This ball, in conjunction with the printed green overlay, creates a level to ascertain the correct orientation of the patient.
View 2 shows a cavity molded in the part to house the level ball which is then covered by a clear overlay.
View 4 shows a cut-away of the part with the steel weldment inside.
Once we have trimmed the part, we then foam-fill it for additional structure and stiffness.
Footboard Also Twin Sheet Formed
This Footboard is also twin sheet formed, and used on the bariatric bed system. As with the headboard, its function, in addition to being a footboard, is to provide a handle to move the bed. this part also employs the same use of “insert molding” incorporated into the Headboard and Side Rail parts.
This mold also utilizes the same articulating core pull feature. To reiterate, this core pull feature positions the weldment correctly during the process. After the molding process completes, the core pull then retracts to allow de-molding.
Additional Footboard Features
View 2 illustrates a pressure-formed feature with internal wiring. A remote control that manages the functions of the bed is docked in this feature.
View 3 is of a separate twin-sheet part. This part, which houses an Information Pouch, is assembled to the Footboard.
Once the part was trimmed, we foam-filled it for additional structure and stiffness. Finally, we attach a colored polycarbonate overlay in another pressure-formed recess.
Benefits of Experience and Foresight: ATI’s Design for Manufacturing Case Study
We at ATI are huge proponents of the Design for Manufacturing philosophy. Additionally, we are innovators that push the envelope in the world of thermoforming manufacturing. Our uniquely trained and specialized engineers can anticipate design problems and offer practical time and money saving solutions. By becoming involved early in the design stages, we are able to spot potential problems before the become problems. As case in point, we chose our twin sheet thermoforming process, a relatively new process, for this project. Many engineers and designers are unfamiliar with the twin sheet process. Our decision became pivotal in providing solutions to client challenges, thus ensuring the product could be manufactured. Importantly, the goal is always to manufacture – both effectively and aesthetically – without expensive retooling and retrofits.
Challenges We Faced
Sizewise, the parent company of Wheelchairs of Kansas, had contacted ATI to design and manufacture Headboards, Footboards and Side rails for bariatric therapeutic beds. At ATI’s suggestion, we retained Samson Design, a design house in Boulder, to engineer and assist with design. Our goal was to achieve a set of parts that were visually distinctive, strong and cleanable. Additionally, the parts would need to house some functional components such as electronics and monitoring devices.
We were faced with determining how we could construct these adjunct components to be durable enough to handle various use and weight issues, while also maintaining a high aesthetic quality. We also discerned a few other complications prior to manufacturing that needed resolution. The first of these challenges included resolving differing rates of thermal expansion between varying materials. Next, we needed to position holes in the steel weldment relative to the plastic part. This placement helped us to achieve a countoured, radiused appearance that looked smooth and allowed easy cleanability. Thirdly, we needed to resolve draw-ratio issues for the Hand Control Docking Station. Lastly, and most importantly, we needed to solve these issues and keep the project within their budget.
Solutions
Strength
Working with Samson Design and Sizewise, ATI chose to manufacture the Headboards, Footboards and Side rails using the twin sheet thermoforming process. This process allowed us to insert mold aluminum or steel weldments inside the parts for added stiffness and strength. In addition, we encased them in a 2 part urethane foam. This helped to prevent rattling and provide additional strength. Additional benefits were the addition of sound deadening properties, while maintaining the desired aesthetics and ease of cleaning.
Resolve differing rates of thermal expansion between varying materials.
To insert mold aluminum and steel weldments in the various parts, ATI had to figure out how to accommodate the differing rates of thermal expansion that the aluminum and steel would have relative to the plastic. When we mold plastic, the sheets are at around 300°F and the weldments are at room temperature. ATI made adjustments for the temperature differences, to avoid the undesireable result of having the plastic cool around the metal. This would result in breakage or could potentially promote failure later on.
ATI accommodated this temperature difference by providing adequate clearance between the “legs” of the panels and interior features of the panels and the weldments. This then presented the challenge of how to hold the weldments in place during the forming process. To solve this, ATI used custom articulating “core-pulls” on the molds to hold the weldments in place. We were able to then retract these “core pulls” for de-molding. In addition, we also had to develop a process to hold the weldments in place during the foaming process. We achieved this by incorporating centering fixtures into the foaming fixtures.
Lastly, ATI successfully developed a way for the steel weldment to fit together inside the side rail during the foaming process. This was crucial for the side rail to function.
Position holes in steel weldment to plastic part.
ATI had to locate the steel heel plate on the side rails precisely to the molded plastic so that it could mount properly to the bed frame. (See view #3 of Siderail above). To do this, ATI developed the part’s geometry to allow registration with the foam fixture. The addition of the 2 part urethane foam inserted into the part positively locates the weldment in relation to the side rail.
Smooth Aesthetics and Easy Cleanability
The client needed an aesthetically appealing look along with an easy to clean surface for the medical environment. The challenge we face in the twin sheet process is that the weld line between the two sheets protrudes outward. We needed to find a solution without causing potential weakening of the structure. We were able to achieve the required finish by developing a concave weld trim. (See view #1 of headboard illustration above.)
To prevent a weak weld, we developed a “heated pinch-line” in the mold. We devised this change for the purpose of keeping the sheet at weld temperature while the weldment is being inserted. ATI was successfully able to initiate this novel approach, despite the commonly held belief that it is too difficult to be done in the thermoforming industry.
Resolve draw-ratio issues for Hand Control Docking Station.
(See view #2 of Footboard above). The draw ratio in the areas for the internal electronics presented an issue. We were able to modify the part design to allow more robust material distribution in this region.
Additional Design Solutions
Additionally, ATI assisted in material selection. We were able to source a material that was tough, and met the UL94V0 flame rating. Of equal importance in medical thermoforming, the material possessed anti-microbial properties.
Finally, we contributed to best practices in inventory control by limiting additional molded SKUs for the Siderail. Only two of the four side rails include a molded feature that is necessary for the “level” features. (See view #2 of Siderail above). ATI decided to mold that feature into all four parts. We then used the polycarbonate overlay to cover it on the two parts not requiring it. This reduced the number of molds required.
Results
Because of ATI’s extensive involvement in design phase, the product successfully rolled out without any field issues. Further, we were able to deliver all modifications and solutions on-schedule and without any budget increases. This was due in large part to ATI’s design-for-manufacture process.
