Friday 26 July 2024

Rule of Thumb: Dealing with Weld lines in Polymer Injection Moulding

Hello and welcome to another Rule of Thumb post. Today we discuss how to handle weld lines in polymer injection moulding. 

Check out my other posts on this topic here.

In a lot of plastic part designs, welding lines are unavoidable, especially if your design has holes. The biggest downside of weld lines is that they impact the aesthetics and strength of a plastic part. However, we can minimize them, move them, and increase the strength by following the recommendations presented here: 

  • Mould and Material Adjustments: Increasing mould or material temperature can improve flow and supports better entanglement of the poylmers at the weld position.
  • Gate Placement: Strategic positioning of gates can influence the location and appearance of weld lines. Changing the gate position can results in moving the weldline to a more hidden position. filling simulations such as MoldFlow can support you to find the optimum gate location even before making the tool. 
  • Part Design: Modifying wall thickness or creating a single flow path can help to eliminate weld lines. Changing the wall thickness will shorten or elongate filling time and thus moving the weld line. 
  • Runner System Optimization: Reducing runner dimensions allows you to increase melt temperature and prevent weld line formation due to better polymer entanglement (see number 1).
  • Injection Speed: Increasing injection speed will lower the filling time, prevent a too early cooling of the melt and potentially reduce as well as move weld lines.
  • Material Selection: If possible, considering a lower viscosity or lower melting point polymer can enhance flow properties.
  • Post-Moulding Machining: For critical areas, machining of the desired part features such as a hole after moulding, can be used to remove weld lines entirely.

Figure 1 summarizes the aforementioned points.

Figure 1: Overview of the considerations for minimizing, and/ or moving weld lines, as well as increase weld line strength.

While these methods can be effective, it is essential to consider the potential impact on other product characteristics and manufacturing costs.

Also, before implementing any of these techniques, consulting with a plastics expert helps to avoid unintended consequences.

Check out my other rule of thumb posts here.

Thanks for reading and #findoutaboutplastics

Greetings,

Herwig 

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

!NEW! Ultra and High Performance Polymer Selection - new online course coming soon - join the waiting list

Literature:

[1] https://www.crescentind.com/blog/8-ways-to-fix-injection-molding-weld-lines#:~:text=Increasing%20the%20temperature%20of%20the,an%20opening%20called%20a%20gate.

Tuesday 16 July 2024

Polymer Selection Funnel Example - Panhandle (Consumer Goods Material Selection)

Hello and welcome to another material selection example using the Polymer Selection Funnel method (POMS-Funnel-Method; in detail explained here and in this video). Aim is to select the optimal polymer material for a panhandle which most of us are familiar with and have in our kitchen. 

Figure 1 presents the four different stages of the material selection funnel and this overview serves us as a guideline.

Figure 1: Polymer Selection Funnel - overview of the four different funnel stages .


Polymer material selection for a kitchen panhandle

This panhandle is used in professional environments as well as in everyday life kitchens (Figure 2). It needs to cover a range of requirements which we understand better by following our polymer material checklist which consists of 12 sections and can be downloaded here

Figure 2: Overview of a pan with the handle. Aim is to select the optimal polymer for this handle. 

Funnel stage 1: Material selection factors

In the first Funnel stage we focus on gathering and understanding all the requirements of the panhandle

For this product, the minimum requirements according customer specification are:

-Continuous operating temperature (long-term heat resistance): 130°C

-Short term heat resistance: HDT-A between 290°C and 320°C

-UL94 fire rating: HB at all thickness levels

-Good stiffness level at elevated temperature: min 5 GPA storage modulus at 100°C

-Food contact approved including EU 2011-10 and FDA

-Dishwasher use proof

-Good surface appearance (black color)

-Economical: handle must be produced using water coolable moulds with high productivity 

-Product Carbon Footprint: < 7  kg CO2/kg

-Easy cleaning an low sticking properties

-Good impact performance in case of dropping the pan

Furthermore, in Table 1 we summarized all important requirement information (requirement worksheet).

Table 1: Requirement worksheet for the panhandle. 

Funnel stage 2: Decision on thermoplastic or thermoset

Reflecting on the must-have requirements which need to be fulfilled, thermoplastics present the optimal choice. Thermosets will struggle with the food contact regulations, together with the mechanical properties, in particular the impact performance, since they are hard and quite brittle. However, There are Bulk Moulding Compounds (BMCs) such as the BMC 1000 from LyondellBasell Industries which use Unsaturated Polyester as base polymer, have food contact approval and may be a suitable grade for this application. 

Amorphous polymers are transparent and have good temperature and mechanical performance. They are prone to stress cracking, have a lower chemical resistance (dishwasher cleaning agents) and their fatigue performance is lower compared to semi-crystalline polymers too. On the other hand, semi-crystalline engineering polymers have good high heat performance, together with good chemical resistance and mechanical properties. 

After this analysis we can make a preselection of suitable grades which can be discussed in Funnel stage 3. 

Table 2 lists all selected grades and their commercial suppliers. The pre-selected materials are PPA with 40 wt% glass fiber (Amodel® FC-1140 L;  Syensqo), PA 4.6 with 30 wt% glass fiber (Stanyl® TE200F6-FC; Envalior), PPA+PA blend with 50 wt% glass fiber (Omnix® FC-4050; Syensqo), and UP with glass fiber loading (BMC 1000 FC; LyondellBasell). 

Table 2: Overview preselected grades and their commercial suppliers.

Funnel stage 3: Selection discussion with worksheet (qualitative matrix analysis)

In the  third funnel stage the matrix analysis takes place. We use the qualitative decision-making process to rank the preselected polymers from Funnel stage 2.

First we access the online tool I developed to facilitate this step here (Polymer Material Selector V1.1). Alternativ, you can reach out to me and i will provide you with an excel version of it. I only considered the must-have requirements. 

The qualitative matrix analysis has three major steps: in the first step we rank how good each material can fulfil the requirements (0 to 5=best), followed by an assignment of the priorities to each of the requirements (0 to 5 = highest priority). The two steps can be done in reversed order too. In the third step we multiply the requirement fulfilment with the priority and add the values up. 

Table 3 summarizes the outcome of the qualitative matrix analysis.

In our case, PPA-GF40 (score: 173 points) and (PPA+PA)-GF30  (score: 157 points) rank number and number 2 respectively, followed by PA 4.6-GF30 (score: 144 points). All three materials should be validated in the Funnel stage 4. Due to the thermal shock and impact performance needed for this application, UP-GF (elongation at break between 0-1.6%) may result in a too brittle material choice and will not be further tested. 

Table 3: Qualitative matrix analysis for the panhandle. 

Funnel stage 4: Testing, selection of material and vendor

Part and system components, as well as  application specific testing with the PPA, PPA+PA, and PA 4.6 materials from Funnel stage 3 takes place in this final Funnel stage 4. Also, processing and tool making are checked to avoid unseen hurdles in the production at a later stage. Final material selection and vendor selection can be done once all the results are obtained.

In our case, we selected the PPA-GF40 for the premium consumer goods segment and the (PPA+PA)-GF30 as  a more cost-efficient solution for the standard segment. PA 4.6 can be considered for the standard segment too. 

Conclusions

In this example we showed the application of the Polymer Selection Funnel methodology for selecting the optimal food contact grade for panhandle. It is a systematic approach with a resin-agnostic view allowing to consider different material choices. 

More polymer material selection examples using the funnel approach can be found here: 

My online selection tool: 

Polymer Material Selector V1.1

Thanks for reading and #findoutaboutplastics

Greetings,

Herwig 

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

!NEW! Ultra and High Performance Polymer Selection - new online course coming soon - join the waiting list

Literature:

[1] https://www.lyondellbasell.com/495bd8/globalassets/products-technology/advanced-polymer-solutions/technical-data-sheets/bulk-molding-compounds/bmc1000.pdf

[2] https://www.matweb.com/search/datasheettext.aspx?matguid=92fbe362c23e4f248abc812a859eb21e

[3] https://www.matweb.com/search/datasheet.aspx?matguid=c9a9ff9a99ca46df81c2e21178e0f2ed&n=1&ckck=1

[4] https://plasticsfinder.envalior.com/en/application/datasheet/2rQz4




Thursday 4 July 2024

Polymer Expert Talk with Dr. Julian Lotz, co-founder and CEO BIOVOX GmbH: "For us the main point is having bio-based content in the materials, getting away from fossil resources and use more renewable resources."

Hello and welcome to this  Polymer Expert Talk, together with Dr. Julian Lotz, CEO and co-founder of the medical grade bioplastics start-up BIOVOX GmbH from Germany. 

In this talk we delve into the promising field of bioplastics, particularly within the medical industry. Julian, with his background in mechanical engineering and fiber-reinforced plastics, transitioned his focus towards sustainable, biocompatible materials due to the profound environmental impact of plastic waste in medical settings. Central to the discussion is the classification of bioplastics into bio-based and biodegradable categories, with BIOVOX emphasizing the development of bio-based materials to reduce dependency on fossil resources. 

They have innovated Poly(lactic acid) (PLA)-based compounds. Their versatility allows them to be used in single-use medical items, due to their high stiffness, strength, and transparency, and are expanding their portfolio to include bio-based Polyethylene and other polymers for a range of applications, including packaging and medical devices.

Polymer Expert Talk with Dr. Julian Lotz, CEO and co-founder of BIOVOX, offering medical grade bioplastics.

**Julian Lotz:** "Let's take this knowledge that we have about biocompatibility, risk management, medical devices, and start making plastics better than we have in large quantities already out there." - This quote underscores the foundational aim of BIOVOX: leveraging their expertise in biocompatibility and medical devices to improve the sustainability of plastics used extensively in the medical field.

Julian highlighted BIOVOX’s effort in addressing the ecological footprint of medical products through life-cycle analysis, aiming for solutions that balance performance with sustainability. The conversation also touched upon the concept of a circular economy within the medical field, underscoring the potential for bioplastics to contribute positively given their inherent biocompatibility and the feasibility of circular end-of-life options like incineration within a carbon cycle. A significant part of the discussion also revolved around the misconception about bioplastics’ impact on food supply, with Julian clarifying the minimal land required for bioplastic production and its benefits over conventional crop usage like cotton. 

Our exchange offers a glimpse into the thoughtful consideration BIOVOX puts into developing bioplastic solutions that are not just sustainable, but also practical and scalable, addressing both the environmental impacts and the specific needs of the medical industry.

Watch the whole exchange here or below.

Here you can get in touch with Julian and the BIOVOX team.

Thank you Julian and the whole BIOVOX team for this great exchange!

Thanks for reading and watching!

Greetings, 

Herwig 

Interested in my monthly blog posts – then subscribe here and receive my high performance polymers knowledge matrix.

!NEW! Ultra and High Performance Polymer Selection - new online course coming soon - join the waiting list